I do the same -- flavorful descriptions of a goofy fail, but no mechanical effects.

I don't have any specific rules for a Nat 1 but depending on the situation I may have the player experience a minor penalty like drop a weapon, fall prone, or deal 1 point of damage to themselves, etc... I don't use this every single time, usually its in relation to when my players are describing more and more intricate combat actions or when they're in an easier encounter. 

I do not do critical fails per se but trying to intimidate with a a 1 roll and a really low over all score will have repercussions.  I will say we do run with a Critical Fail on saving throws rules which allows for critical damage.  It is amazing wonderful yet also amazingly brutal when it happens.

I used fumbles until the fighters gained Extra Attack. Now they are inconveniences but still fails, even if you would have hit with bonuses.

Some people feel like if the PC is skilled enough, they should never fail. But that is not realistic. Even the best professional in any realm can fail sometimes.

My nat 20 is max damage on the base roll and roll the doubled dice. So 1d6 crit is 6+1d6. It seems to work well and I never have to worry about the party getting excited and the damage comes up double 1s.

I tend to use what is going on with the battle and base it off that.

If there's an ally next to the targeted enemy (and within range of the attack), they might get disadvantage on the next attack because they are distracted by their teammate flailing wildly nearly them. If their weapon is a mace, it might swing down and hit them in the toe and do 1 damage to the attacker (never an actual damage roll). If they are near a loose stone wall and it's a ranged attack, the shot goes so far wide that maybe it causes part of the wall to crumble. Maybe the battleaxe gets stuck in the mud because they swung so poorly, and they cannot take reactions as a result.

All low-level problems, with imposing disadvantage or maybe falling prone being the worst options. Never rolling on a table, just giving some extra flavor with occasional mold consequences.

I never use fumbles.  I've played characters in games where the GM was running critical fumble rules and it has always disproportionately punished any character who depends on attack rolls in combat and gets worse the more attack rolls they make.  Too many times I've seen something happen that completely shuts down a character for a combat, whether they lose (or destroy) their only weapon that can harm the monster they're fighting or they injure themselves and take some sort of penalty for a time.

I will say, I am far more prone to use crit fail consequences for my enemies than I do for players (for one thing, the only game I'm running currently has a party that is 2/3 halfling). A goblin crit misses, played off as swinging so wildly it is unclear who he was aiming at, and so the ogre it is attacking next to makes their first attack against the goblin because it is thrown into a rage by the recklessness of the goblin's sword strikes.

You have to balance the negatives of the 1 with appropriate positives on a 20.  Using a generic table is boring.  I try to tailor the consequence to the situation.  Do it right and your players will look forward to the 20s and the 1s because something interesting is going to happen.

Make sure the positives on a 20 slightly outweigh the negatives of a 1.

Monsters fumble and crit too!

Quote from Wysperra >>

I used fumbles until the fighters gained Extra Attack. Now they are inconveniences but still fails, even if you would have hit with bonuses.

Some people feel like if the PC is skilled enough, they should never fail. But that is not realistic. Even the best professional in any realm can fail sometimes.

My nat 20 is max damage on the base roll and roll the doubled dice. So 1d6 crit is 6+1d6. It seems to work well and I never have to worry about the party getting excited and the damage comes up double 1s.

 
I think this is the best way, artificial tables add extra bookkeeping, but also become predictive. A 1 is always a failure be it in combat or in any other test, a 20 I use the Crit rules in the game, double dice. If that means a lot of dice then sometimes my table doubles the dice roll instead just to keep things flowing a little quicker, sometimes criting and then rolling bad rolls makes for a fun narrative around the table. I have played in a game where when you critted the DM let you re roll ones, there is a feat I think that lets you re roll ones and 2's for damage, that then got buffed to reroll 1,2, and 3 when you roll a crit just to make it fair on that player. 

Quote from BigLizard >>

One aspect of D&D that is less prevalent in modern editions, but was central to the experience in classic editions was the concept of equipment reliance and the management of equipment as a resource.  There were variations on the concept including things like the use of holy water against undead, wolfsbane against werewolves, garlic against vampires, but also in regards to tracking things like torches, arrows and the quality of weapons.  In a sense, the power of your character, the amount of impact they could have on battles was often more or less, depending on how well prepared you were.

For me personally I have always used durability rules for weapons and equipment, a simple system that ensured that gear would wear down, need replacing, as an extension of this sort of dependency on equipment.  

One way I have always used fumbles and criticals is less so on the impact of the battle but impact on the equipment.  Shields and weapons would break, armor would wear down, that kind of thing.  It would add to the gritty feeling of the adventure, give mundane equipment a greater purpose and create a sense of "preparing" and need to "go to town", get "downtime"etc.  It also gave skills like smithing and such purpose where players could repair and maintain their own gear.

I try not to make this too fiddly, but in any case this is what I use critical hits and fumbles for.

 
For me these mechanics become an irrelevant part of the game especially as players get richer at higher levels, it becomes a simple thing to just pay out and replace or repair mundane armour/weapons. It also makes the game too book keepey, Its why past level 6 I dont care about how many arrows a player has left, or crossbow bolts. I might just periodically ask them to knock of 20 gold to cover ammo costs. Shopping at higher levels is more fun when it is for more specialised things.

if you want this kind of book keeper game Pathfinder or a similar system is probably a better option for you. 

First; if you roll nat 20, you get 1)  DMs choice; get inspiration OR if character has it already -> 2) players choice; auto advantage to next roll or roll d100 for some random positive effect.

Second; if you roll nat 1, you get 1) DMs choice; lose inspiration (if having it), OR -> 2) players choice; auto disadvantage to next roll OR roll d100 for some random negative effect. 

So there are "auto"effects by DM (get inspiration/lose it) and alternative choices for Player to make. 

Honestly, just depends on the situation. I don't do big negative effects all the time on Crit Fails during combat, but if it would result in a funny scenario (idk for example a player just hitting the floor or wall instead of an enemy) I do use negative effects. It mainly just depends on the situation. For ability checks i usually never do crit fails or successes tbh.