TAG before LAG

Some questions that i have been wondering about....

1.If you are beginner should you be tag until you have success, then become lag once you really start to master and understand the game?
(for cash games)

2. In tournaments am I right by begining pag(with say 5000 chip start and blinds at 10/20). Then tag during middle stages. Then i have no idea, best ive done so far was 300 out of 3500.
-Stay tag with some lag(dependidng on chip size)? Question is worded weird...pretty much,
-I do good first 2-4 hours, then end up shortstacked.
-I try to see flops for cheap then go with pot odds and play hands according to position, just can't get over hump...should I be more lag?
-If so, how (examples) and when (always with position)?
-Any moves i should be during that time? Any help would be appreciated, i know it is kinda broad but maybe just assume i am mid stacked? or examples of each small avg big stack? lol this question is long and a lot...sorry...just looking for help

was in paragraph form seperated the different questions.

last one lol
- in tournament play and shortstacked i push with atc if blinds are 1/5 of stack? (heard or read it somewhere not sure if i heard/read it wrong)

focus on the 2 people to your left, and the 2 to your right until you get the hang of the table. notice how often the ones to your right steal your blinds. learn to repop their steals. notice how often the ones to your left defend their blinds. steal theirs. this is where a lot of your chips will come from. the preflop battle for the blinds. learn to mix up how you bet a flop based on the texture when you're stealing. keep them confused and guessing, and theyll fold a lot more.

Read a good book on tournament poker, imo. Try Harrington's.

haha i like this answer, guess good book will answer all those question huh? Was actually at borders yesterday and got overwhelmed and didnt know which one to pick, wanted to get them all honestly, but would of set me back a couple hundred. I did start harrington on hold em' (had it on computer but lost it) and is great book, love the examples and the test setup of it, makes you really think hands through. I will probally will buy it next time im out.