Homebrew Rules

I use a list of homebrew rules that I've tested and developed over the years of dm'ing. If you have any questions about them, feel free to ask.
Flanking
When two combatants are directly across from each other with an opponent in between them, they each get a +2 bonus to melee weapon and spell attacks. For each additional combatant that gets within melee range of the target, an additional +1 is added to the bonus, to a maximum of +5 when encircled by five or more hostiles.
Exhaustion
There is a new instance of when a character will take a level of exhaustion, which is when dropping to 0 hit points and becoming incapacitated. This is to show that constantly being hit hard enough to pass out, or at least become unable to keep fighting, takes a toll. You can't just keep getting knocked down hard and get back up endlessly. A few times? Sure, you are heroes in a fantasy world, but more than a few imposes some serious limitations, as it should.
Short Rests
Short rests can be taken in a few as 10 minutes. Characters can still take an hour if they want to just rest for roleplay or immersion reasons, but 10 minutes is all that's required for the effects of taking a short rest. Features that require an hour of work, that say "this can be during a short rest" are unaffected, as it's the hour of work that's the important part, not the rest. Casters can ritual cast a spell during this time and still benefit from a short rest.
Resurrection
Resurrection is a difficult and tricky process, and is not guaranteed in most cases. When a creature has died, a special hour long ritual must be made to accompany the use of a resurrection spell. In the case of revivify, this ritual still takes an hour, but only needs to be started within a minute of the target's death, not completed obviously. In addition to the person casting the spell, a person with proficiency in the medicine skill must prepare the body and help the caster infuse the body with renewed life. The caster of the spell makes an appropriate spellcasting check (religion for clerics, nature for druids, arcana for lore bards, etc) and the physician makes a medicine check, then the target of the resurrection spell makes a constitution save. The DC for all of these checks is DC 10 + 1 for each time the target has already been resurrected. If the spellcasting check and medicine check both succeed, the constitution save is made at advantage, if they both fail it’s made at disadvantage. If one succeeds and one fails, it has no effect on the save. If the save is passed, the target is resurrected and takes one exhaustion level for each full day it was dead to a maximum of five, instead of the resurrection sickness listed in such spells (revivify imposes a single exhaustion level). If the save was failed, the spirit cannot find its way back to the body, or is unwilling to return, or has been blocked from returning by the gods. Despite the amount of exhaustion you may have had before dying, even if you died from exhaustion, you can never be resurrected with more than five levels of exhaustion. You can't died from being revived.
DM Inspiration
Inspiration can be used for a number of things in addition to granting yourself advantage. Some examples are imposing disadvantage on an enemy, choosing to succeed on a lore check rather than rolling, or turning a standard hit into a critical hit when attacking. Players get one inspiration per session.
Encumbrance
I no longer use the variant encumbrance ruleset, instead going back to standard carrying rules. However, the caveat is that anything that's not worn equipment, like weapons, armor, holy symbol, or something like that, goes in your backpack. This could include food, tool sets, a bedroll, spare clothes, rope, backup quivers, etc, anything that you wouldn't typically wield in combat. Large, adventuring style hiking bags are very heavy and cumbersome, and cannot be carried into combat or athletic activity without penalty. Any character attempting to fight or engage in strenuous athletic activity while wearing their pack has disadvantage on physical rolls, checks, or saves of any kind, and has their speed reduced by 10. Packs can be dropped where you stand using your object interaction.
This is, I believe a way to capture that feeling of needing to shed that extra weight in order to be effective in a fight, while still simplifying the process rather than itemizing everything you have. Though tracking your inventory will still be necessary.
Spell Components and points
The previous system of spell components will now be an opt-in. You can use a focus, holy symbol, or other standard device to ignore components if you wish, or can still use the component system for more realism, and to potentially research ways to use other unique components to alter or empower spells. The rest of the rules for using components when they ARE used, will remain the same as those listed below.
Spellcasting is a difficult and rare gift, and the need for components to aid it is ever-present. This will change material components in a few ways. For starters, I will track each caster's inventory of materials, much like encumbrance. Material components, with one key exception I'll explain in a moment, are always consumed by the spell, regardless of the spell text. Cantrips no longer have material components at all, all cantrips are still free to use. There are no "component" stores in general market areas, your average citizen has no need for them, mages and priests are rare compared to the average person, and usually have a temple or tower that they stay in which gathers and provides these things. Adventuring casters need to source these things as they travel, which can lead to many interesting side quests, roleplay opportunities, and interesting workarounds. Because of this ruling, there are also rumors and whispers that there are even some special components that can enhance or empower existing spells to perform beyond their normal limits for one casting. The exception to this rule is high-value or high-cost components. Any component with a gold cost is NOT consumed by the spell, regardless of the text. This places higher value on some utility spells like continual flame, and the like. This also makes resurrection materials very valuable and sought after. While this may seem like a hefty limitation, I believe this helps add a sense of realism and mystique to spellcasting, while making some spells that are usually seen as "useless" or "sub-optimal" more interesting and fun to use.
While not homebrew, since it's in the dmg, it's worth mentioning that we will use the spell point system, not slots.
Potions
Potions always take an action to drink or apply to another, but use their maximum possible health if a healing potion. In other words, a standard healing potion takes an action, but instead of rolling 2d4+2 for hp recovery, you simply heal for 10, the maximum amount possible.
Leveling Up
I use a simplified point-based level up system. It's similar to many other homebrewed systems like it, nothing overly unique about it. Basically, every level you start at 0 level up points, or LUPs, and when you get to the amount of points that's equal to your next level, you level up on your next long rest. For example, if you are level 2, you start at 0 points, and once you get to three points, you level up to level three on your next long rest, starting over again at 0 out of 4 points. Any points you have that go over your needed amount are carried over, so if you are at 4 LUPs out of 3, you go to level three with one point to carry over, and are at 1 LUP out of 4 now.
Undeath Plague
The status of undeath can be transmitted like a disease. Any time a character is attacked by a corporeal undead like a zombie, ghoul, or wight, if the attack successfully deals damage with a melee attack, the target must make a Constitution save with a DC equal to 10 plus the CR of the undead, rounding down for fractional CRs. On a fail, the target contracts the undeath disease. Once the disease is contracted, additional successful attacks from the same type of undead have no additional effect. You can have multiple different strains at once, however, such as the zombie disease and the ghoul disease at the same time. While diseased, after every long rest the target must make another Constitution save at the same DC. On a failure, the target incurs a level of exhaustion. If six levels of exhaustion are incurred, causing the death of the target, the target immediately rises as an undead of the type that infected it. If the target succeeds at this save while having no levels of exhaustion, they have successfully fought off the disease and no longer require saves on long rests. No magical healing can remove the disease, and disease immunity does not apply, although targets normally immune to disease have advantage on all saves. Once at four levels of exhaustion or more, the target is in it's most communicable and infectious period, and anyone that spends more than an hour in the same room or in close proximity to the target risks exposure, making a save as if attacked. Because of the highly infectious nature of undeath, necromancy is considered one of, if not the, highest crimes possible, worse even than treason.
Soft Magic
This isn't so much a set of rules, as that would by definition make it a hard magic system, not a soft one, and it is loose idea that might come up from time to time. The three prime casters, Wizards, Druids, and Clerics, the epitome of their field in the Arcane, Nature, and Divine respectively, occasionally have their mastery of magic manifested in ways that the other casters simply can't achieve. This doesn't occur in combat, but can happen sometimes in other ways, such as a starving Druid in the wild finding that several berry bushes spontaneously spring up around them to sustain them, or a Wizard that's trapped in a dark room without their Light cantrip suddenly finding that all the candles in the room come alight to five times their normal illumination in response to the mage's distress. These are things that will not have saves, or set rules and descriptions, but will simply happen from time to time as the circumstances dictate.