Most of the time you should raise/re-raise with top-pairs (AA-QQ) and top connectors (AK, AQs) in order to make low-pairs and various connectors pay to see flops against you. Remember, they will often have the opportunity to double up on you if they hit (although many beginners do not realize this and fold too often pre-flop).
Stick to the premium hands. You will pay dearly to chase with second-best hands in NL.
Keep most raises down to between 70% and 100% (making it 3 times the big blind to go typically equals an 80% pot bet) in order to save money when you get re-raised or called by stronger holdings. If there are limpers in front of you, raise to about 4-6 times the big blind.
Have respect for strong tight players (for example, you should drop AQ if a strong player raises under the gun).
When very weak players have entered the pot, be inclined to call and take flops with them.
Texas Holdem Deceptive Plays
Adding deception to your game can be part of a winning poker strategy and is very important because it makes you less predictable. If your checks always mean that you are weak or your bets/raises always mean you are strong, the more observant players will have an edge on you.
When you have a strong hand it is sometimes correct to slowplay. This means just checking or calling on one betting round with the intention of betting/raising on later rounds of betting. In Holdem this is a very common play on the flop, because you want to lure players in and raise on the turn or river where the bets are doubled. This tactic can easily backfire when you let your opponents take free-cards that can beat your hand. Many players slowplay too often and lose pots they would have won had they not slowplayed. When this happens it is mathematical disaster, since you lose a pot you would have won had you bet/raised and now you have to pay off an opponent who has you beat.
In general you shouldnt slowplay when one of the following criterias are met:
A free card can beat you.
A free card is not likely to give your opponent a second-best hand.
There are many opponents in the hand.
It is a large pot