Good question .
For me I first need to know a few things every time I sit down at a poker table. Cash Game or tourneys it does not matter.
1) I am I reading the table the best possible for me and my style
2)Are the table Dynamics right for me or do I need to change it
3) Do I Know what Players are weaker ( easiest for to get chips ) and what players are more skilled then others .
4) What areas do the players like to make moves and can I make adjustments to better benefit from them .
5) What can I defend or play against most styles with out having to shut down and tighten up giving my oppenent the better of me for tightening up too much
6) What type of game strategies do I need to play against this table
7) Can I get a read on this table quick ( is my reading of the players efficient or too slow )
8) This is a good one many have trouble with -- Is my skill better then the others at the table ? If so am I able to have the know how to manuver them to play in my benefit ?
This is just some of what I need to know when playing.
If your using the HUD then you need to know what all the numbers you set things to , to understand them quickly.
You will need to know what each means because this tells
how and what you can possible do (play) with the hand you get and the position your in at that time.
Most of all is being able to be consistant and have the ablility to manuver and adjust to any situation that can come at you when sitting at the table.
There is no solid way of saying this player is this good and this player is this good .
About all you can do is compare players at the table with how they play and react.
Why is this? because poker is and gets so indepth that some things are what I called layered in order to play out that if you dont know where the 1rst layer started you cant understand the moves .
Putting Why on a basic perspective look at it this way one player may be say to lvl 10 on preflop play and lvl3 betting but his post flop maybe lacking down to say lvl 3.Now you take another person who is say lvl 5 preflop but a lvl 9 post flop to the turn but after the turn on the river he dropts down to lvl 2 and his 3 and 4 bets are say lvl 4 lvl 6. To say one person is better then a nother comes to how well they play the game in an all arround perspective.
Long read but I hope you get the just of the post.
Hard work work with understanding and experience then you may notice the difference between your play and others .
Good Skill at the Table