Pre-flop action and starting hands

One of the most common mistakes rookie players make is that they play too many hands. Poker is the kind of game that presents many temptations. Seeing hand after hand how others get hit by the flop on rags, can and will drive players to act on rags themselves, however, if you want to squeeze any long-term value out of your play, that's not the way you should approach things.

The very first thing you can do to improve on your play is to adopt some sort of starting hand selection method. Keep in mind that a good poker player can indeed beat a weak one on rags, but acting only on positive EV will give you much better chances, especially if you know you're not skilled enough for extreme plays.

If you do decide to adopt basic hand selection, you have to make sure you're disciplined-enough to stick to it. The downside is, you won't be involved in many pots, and you'll spend most of the game waiting around for good starting hands. The good side is, you'll have a lot of time to study your opponents, make reads and observe betting patterns.
Exactly which hands you can act on, depends on the number of players you're confronted with. The more opponents there are, the tighter you have to play it.

If there are 9 other people around the table, don't play anything other than AK, and if you get pairs, from 99 upwards. As the number of players decreases, you too can gradually loosen up (bear this in mind when playing in STTs)
When faced with 6 players, unpaired cards you can play are anything from AJs upwards, and the pairs are 66 and up.

If you're in a short handed game, or in a heads up, the starting hand values plummet. In a heads-up for instance, you should play aces with just about anything suited, kings with 9s and above suited, queens with T and above suited, and jacks with 9 and above suited. Play any air you get.

Remember, in a heads-up, you need to become really aggressive on all these hands, as aggression is the key concept here.

What exactly should you do with these hands before the flop? Raise and re-raise on QQ and above, and also on high connectors like AK. You want to make as many players holding low cards, fold as possible.

NL Hold'em is especially unforgiving with those who chase windmills on weak starting hands. Don't commit that mistake.
Make sure your raises do not get out of control. You want to leave some chips if you get re-raised or called.

Limp in with anything weaker than AA, AK, AQ, KK or QQ. you don't want to waste a lot of money on those hands.

Don't forget to mix up your play every now and then. You want to avoid becoming too predictable.