The simple answer to question #1 is NONE.
Live Standard (on chess.com or ICC, or FICS or ANY live chess server) tries to "suggest" a correlation to one's true OTB rating but even then, OTB players are a different species altogether. While one can argue that strong tournament-rated OTB play is indicative of strong online play at similar time controls ... the reverse is not at all true as the committment/discipline levels of a regular (plays every week) 1200-tournament player are miles ahead of a 1600-1700 online player who monkeys around with 3-min blitz (or even slower time controls) on-and-off during the day while eating a bag of chips / checking messages on their phone.
Trying to match ratings between different systems and/or rating pools is really just approximating ... but for what? I don't really see the benefit of this exercise. If you want to know how good you are at Federation rated OTB, go sign up and play one! :)
To your other question: Improving one's performance (and therefore, over a long run, their rating) is a mix of a lot of different factors. Tactics tends to be the really big slice of that pie-chart for club players ... so yes, a tactics-heavy diet of chess preparation will definitely be an efficient way of getting you closer to a rating goal. You do want to supplement that with other stuff as well ... but at the club levels, you will lose more games due to missing tactical shots than any other mistake.
Well i have, basicly, a couple of questions. The first one is which of the three different ratings we use in chess.com is more representative of our real fide elo rating? bullet, blitz or standart?
my second question has to do with a post i read a while ago about someone who sky rocketed his elo rating to 2045 mainly by solving tactics and studying endings. so if im around 1700 standart should i focus mainly in this to aspects of my chess studying?