As a DM there are two house rules I always play with:One of my favorite things to do as a DM is to fiddle with the RAW to adjust them to my liking. And I am sure that most of you do too. I always like to hear what other people come up with in that regard. It is great inspiration and sometimes you find a well thought out houserule that you ask yourself how you could have ever played without it.
Therefore I want to ask you, what your favorite 5e houserule is, that you just can't live without anymore.
1. Picking up a weapon off the ground takes an action. You can kick it with your free action, but you need to use an action to actually pick it up. Drawing a weapon from a scabard is a free action and dropping a weapon is completely free. This has a substantial effect on gameplay, for casters in particular. As a player, most DMs I play with have not implemented this, however one of my normal players wanted to try and DM a game with our group and me as a player and she did implement it. I found out when I tried to pick up a weapon off the ground ... what is good for the goose!
2. I allow versatile weapons to gain -5 hit/+10 damage from GWM if they are wielded with 2 hands. This does not affect gameplay that much. Usually the only thing it does is let the one player who always gets this feat use magic longswords when he would otherwise not. This could be a big boost for a Monk with spears and staffs, but I have not had that at my table yet.