seat belt fastened when seated, incase of turbulence

don't drink coffee (or water stored in the plane tanks due to bacteria concerns), only canned/bottled drinks

bring earplugs (loud noises) and mints (bad smells)

I always sit fairly close to an exit. I hope I never have to make an emergency evacuation, but I'd rather not be stuck behind 40 other people.

Use the restroom no later than 45 minutes before landing, to avoid the last-minute rush.

My habit is to check my belts when the FA mentions it and look for the nearest exit, counting the rows in case of limited visibility.

I don't even need to be paying attention, my subconscious just picks up the words and I check.

This thread might convince you to start... Overhead cabin theft?

I don't cross my legs on takeoff or landing, because that could lead to increased injury during a crash. I put everything away that could become a projectile.
I make sure I am awake for both takeoff and landing because if there is an incident I want my brainwaves in a fully aware state.
Shoes stay on below 10k feet.
I note the exit in relation to where my seat is.
Belt stays on whenever I am in my seat.

For me, it is a few simple things.
1. On my way to where I am seated, note where the exit is.
2. Once seated, buckle up (stay buckled up from gate to gate) and read the safety card.
3. Pay attention to the safety briefing.
4. Keeping your carryon under the seat or in the bin.
5. I prefer to keep my shoes on, the way the floors are on a plane, the CDC would say a few things about that.

The only cautious thing I do on planes is keep my passport on my person and I'll keep my camera/laptop bag by my feet instead of the overhead bin on longer flights that I plan on sleeping on.

Use restroom shortly before takeoff. On a long-haul, use it 1 hour before arrival.
Seat belt fastened while seated.
If I'm in Y, I prefer to be *in* the exit row. If I'm in J or F, I note where the exit is. (It's usually not too far away.)
Passport always with me, not in a bag. Same with my phone and wallet. If I have to evacuate, I will have no hesitation or temptation to jack around with a carry-on bag. It seems like most recent evacs include stories of people either digging through bags for their phones or taking the bags onto the escape slide.
Carry a decent-sized charging brick. I don't assume that in-seat power will work, or that my adapters will necessarily work well or at all in foreign airports. (I guess this is less about safety and more about avoiding getting stuck with a dead phone.)
I always have my shoes on unless it's a *very* long-haul flight, and then they're back on well before landing. But I've never consciously thought about it.
If I'm boozing, I two-fist with water and stop drinking everything except water pretty early in the flight.

I keep my shoes on during takeoff and landing, not due to dirty floors but because I'd prefer to have shoes rather than bare feet in an evacuation. Also I count the rows to the exit. I do keep my passport on me usually - I'd rather it not be stolen but also will help to have it after an emergency landing or crash.

I NEVER put hand luggage in the overhead lockers. Although if I'm on overnight long-haul domestic Russian flights (SVO-IKT/KHV/YKT/VVO) I'll always sit near the back and take the pair of seats to use the 3rd seat in front for storage. Related to that, I NEVER check luggage in. I've only ever done it flying to JFK and MCT (my first ever holidays) and moving to/from Saudi Arabia/Russia

Passport/phone always with me.
Seatbelt always on.
Always in an aisle seat if possible.
NOT bothering cabin crew about where my seat is (unlike a HUGE number of Russians)
No tea/coffee (I hate coffee anyway) on board.
Earplugs and eyemask, especially for overnighters (and even more so for eastbound Russian trips)

I don't fly in loafers, or any shoe that could be knocked off my foot easily in an urgent situation.

I uncross my legs for takeoff and landing and sit with my hands on my knees, legs apart. It's harder to get out of a wreck with two broken legs, and it's easier to break your legs if a bunch of seats and cabin fixtures go crunch into crossed limbs.

I keep everything important in pockets on my person: wallet, keys, passport, phone.

I plan an escape path to the nearest EE, and also take note of people around me that might need help in an emergency: elderly, small kids, etc. I never assume an FA will be anything but useless in an urgent situation. For every heroic story I have read, there's one or more of FAs breaking down weeping or going catatonic when it matters.

Everything in the overhead is locked unless for some reason my laptop bag can't go under the seat. (There's no way to lock my laptop bag--the one flaw in an otherwise good bag.)

Passports and cash are always on my body, never even under the seat.

Seatbelt unless I need to get up. If I'm trying to get some sleep it might be quite loose.

Shoes unless we are at altitude.

I note where the exits are--not by counting but by what is around them. Counting in an emergency would be hard anyway. I do not worry about which is closer--in practice you're going to have to go with the flow. Swimming upstream to a closer exit is almost certainly going to take longer.

Mints are a bad smell especially on the breath of someone next to you on an airplane, at a concert, etc. Similar to perfume, cologne, etc.