Be On Time
Seriously. Being late just delays everybody else.
If you can't be on time (because lets face it: real life interferes sometimes), let someone know. A 5 second text message can save the rest of the table a lot of time in waiting and concern that you got into a car accident.
Keep Track Of Your Own Stuff
That means things like your HP, any limited use abilities, and so on. It also includes your character sheet, as forgetting that tends to create a lot of delays and guesswork.
The GM can't know everything about everybody all the time, so if you know your own current HP and how much armor you have with buffs, that's a big help.
Don't Keep Track Of Other People's Stuff
Don't spend a lot of effort trying to write down things like how much enemies hit for. It could change pretty quickly if I use a different ability or get different rolls, and trying to track it for you is just wasted effort.
It can also lead to mistakes if you assume it's doing X because it did that before, only this time I maxed out a roll and now it's doing Y. Or if it poisons you but didn't poison someone else for some reason.
That also goes for other players. They can keep track of their own stats, you don't have to write everything down all the time.
(One exception is if the party has a shared party inventory. Someone has to keep track of that for everybody.)
In games where your stats can change significantly due to some ability you have, plan ahead and prepare those stats ahead of time.
Druids in D&D 3.5 are a classic example. Wild Shape lets them change into animals, which causes them to use new stats, that aren't quite the same as the animal stats in the Monster Manual. This involves some math, which can get significant and make your turn last a very long time. If you have favorite animals you turn into all the time, have those stats ready ahead of time so there's no math. (Ditto for Summon spells.)
If you run around with five buff spells active, know what they do. There will be times when you have to figure something out, but you shouldn't have to do it for your most common abilities that you're always using.
If the fastest way between A and B is a straight line, but you want to go explore and take the scenic route... do that! Making things easier for the GM doesn't mean you have to just follow the most direct linear path between plot hooks as you possibly can.
It's the players who are playing, and part of the fun is that you can go off and explore the world. If that winds up changing the plot, then it winds up changing the plot. In my experience, players are infinitely creative and tend to find ways to deviate from what the GM expects anyway.
If exploring is something you find fun, do it. The point of the game is to have fun, after all.