Texas Holdem Strategy
I will be focusing on strategies that work best in tournament style poker. While most of what is talked about carries over to cash games there are differences between the two that will be talked about in another guide.
The most important thing new players underestimate even if they hear it all the time is position. During a tournament, position is as important as the cards you are dealt, and in fact heavily influences what cards you play. Many hands you play from the dealer position would be unwinnable in the long run from the small blind post flop just due to the order players act.

A player in the small blind will always be out of position while a player on the dealer button will always be in position. Other seats may be in or out of position depending on who enters the hand behind them. Players under the gun will have four to five people acting behind them with position on them and so their hole cards are normally at the top of a players range.
On the other hand, the dealer and the player to his right to cutoff will be opening with a much wider range of hands, as the dealer is guaranteed position and the cutoff only has one player who will have position on them if called.
When playing against an opponent you aren’t trying to guess their exact hand but instead put them on a range of possible hands. There are multiple reasons for this, a big one is because putting them on an exact hand is impossible on the flop and turn and is only an educated guess by the river.
The reason to put someone on a range of hands is to help you know when to call or fold by comparing their possible holdings to your own. Another reason is it allows you to notice play that makes no sense based on what they may have, allowing you to catch bluffs with non premium hands.
As the hand progresses you narrow your opponents range based on the board and their actions. The first steps of determining their range is to look at their opening position. Someone who opens the betting under the gun has the top of their range, likely hands like pocket 10s to aces, ace king or queen. Even a player who isn’t tight in their opening ranges wont get much weaker than ace 10 or high suited connector like ten jack.

Further down the table if it folds to the button, their hand range is much wider. The dealer can open with 30% + of their possible hands depending on how tight they want to play. You will need to be paying attention to how often a player raises when folded to in dealer position to get a better idea of their range and play style.