Don't buy in short-stacked.You want to have enough money in front of you so your decisions don‘t become "binary" -- in other words, a choice between all-in or folding. Try to buy-in for at least 100x the big blind amount, so in a $1-2 game, that would be $200.
"Poker is a lot like National Geographic"Mark Seif compared the game to a nature show. He stresses that you should come to the poker table hungry, like a predator looking for their next meal. Look for the weak players and take full advantage of them. You must also never feel bad about taking all the money you can off other players, that should always be your goal: to take it all.
Be proactive about getting in the best game, with the best seat.Don’t be shy about asking for a seat change or table change. You ideally want a seat with aggressive players to your right, passive to your left, and remember money flows clockwise around the table. On the other hand DO NOT switch seats because you think your seat is “unlucky” or another is “hot” -- there is not such thing. And any player you hear doing that? That’s your next meal.
You must always pay attentionWhen you sit down, don't post your big blind early. Wait for your big blind to naturally come around and use the time to observe. Identify what types of players are at the table and especially pay attention to people’s betting patterns. Notice what kind of pre-flop bets will get people to fold and which won’t. Who are the aggressive players? Look for tells and listen to what people are saying. Some players will tell you exactly what they had and why they played a hand the way they did. Poker is a game of incomplete information, and the more information you have, the better you'll be able to make the correct decisions.
Master the oddsMake sure you understand how to calculate both your outs and the pot odds. It is also important to understand implied odds. This is a key skill for every winning player, and without it you cannot make correct decisions.
A side point: Always take any edge every time -- even just a 1% edge.