Most new players tend to play too passively and opt only to check when they have the chance or to call an opponent's bet. They also tend to "limp" pre-flop, ie, to match the big blind rather than raising it up. This allows other players to enter a pot cheaply and possibly out-draw you.
During the Poker Basics course, you have learnt how to assess your hand, both pre-flop and after the flop, and also how to determine whether you have a draw or a made hand, and what to do with it.
There is one more crucial thing to add: Don't be afraid to use your knowledge while you are playing. Don't have a crisis of confidence. In short: play with conviction.
BACK YOUR JUDGMENTThe best strategy for the tight-aggressive player is usually to bet or fold. You should spend your time around the poker table trying to determine what cards your opponents are holding, and how they compare against your own. If you think you have a better hand than your opponent, you should bet or raise to build a big pot. If you think your opponent has a better hand, you should probably fold and lose the minimum.
Calling suggests uncertainty and it gives your opponent the chance to make a bluff against you. It also suggests that you have not thought hard enough about the state of the pot in progress. Rather than taking an uncertain middle route, calling or checking, you should have the courage of your convictions: bet if you have it, fold if you do not.
TWO WAYS TO WIN A POTBetting and raising are also preferable to checking and calling because they give you another way to win a pot. In order to win a pot at showdown, you must have the best hand. But you can also win a pot if you manage to persuade all of your opponents to throw away their cards. If you are the last player to remain with cards, you will win the pot without a showdown.
Only betting and raising gives the opportunity of a pot ending before showdown. If you only check or call, you must have a big hand to stand any chance of winning.
This is why you should play with conviction as part of a tight aggressive strategy. Choose good hands to play and play them hard.