1) what is a compliance officer
- in lay man's term - a policeman in the company, to make sure everyone else follow the rules/guidelines set out by authorities.

2) How do you improve your drafting skills and what documents do you normally draft. Some 600 pages contract or 6000 pages Articles of Association?
- if you realize, even now I am drafting and thinking how to respond to you.
- there are various types of agreements out there, (assuming your employed in a sector) try narrowing down the type of agreement... example service level agreement.
~ look at the structure of the agreement, if you have look at various agreement, you will see a recurring theme. example - duration, termination, obligations etc...
~ understand the need for specialize clauses (meaning you need to understand your own industry/sector). You need to know what your doing.
~ finally boiler plate clauses (this are standard clauses in an agreement). example assignment, entire agreement clause, amendment clause etc...

3) Actually the more viable route would be to practice after that go for in-house. Of course a 10-15 years experienced lawyer would be quite valuable in-house.

If you ask me, having either litigation or conveyancing background is a must. However, having both will give you an edge. Corporate experience on the other hand is optional.