What is the best way to learn tactics?

The title says it all. I do have multiple chess books, and they are quite useful. Unfortunately, books cost money, so i was wondering what is the best free way to learn tactics otherwise. Is there a website dedicated to it? or is the best way to watch master games? or is it just to play? or perhaps a chess teacher? I would like to get better at tactics, as when I analyze games afterward with an engine I frequently notice that I often make the "obvious" move, rather than the more destructive, subtle attack. In summary, I would like to know the best and most productive way to improve tactics that is free or extremely cost effective. 

PS: I have no need to study openings and endgames as of right now, most games my level end far before the game enters endgame theory. I know the most basic openings (kings pawn, italian, sicilian, kings indian, french), but see no practical need to learn the tedious openings

Thanks to everyone!

Chess.com would prefer that you step up to a diamond membership which would allow you to do unlimited TT puzzles, do the tactics courses on Chess Mentor and watch related videos (IM Danny Rensch just finished a killer series reviewing all the tactical motifs).  That's a lot for $100 a year.  You said free though.... Staff frowns on recommending rival chess sites, so I won't, but I bet a little googling around would yield a free tactical trainer site.

If u want a free way, do the daily puzzle on chess.com and the 3 free tactics trainer every day.

Maybe joining a chess club. I've been to a few chess club meetings at my school and have learned some new tatics that have helped me. 

Thanks Dargone i have looked into the book and i am thinking about buying it. I also found a cool little website literally chesstactics.org, that neatly explains a lot about tactics (its not a joinable website). It shows how to effectively fork, skewer, xray, etc. I would recommend it to anyone looking to brush up on their skills. Thanks for the information guys

Joining a chess club may help, even in a tournament. You will learn many things when you look at master's games or even your own games. :)

Chess.com staff guy (forgot his name) mentioned a system a year or so ago.

Forgot the specifics, but the idea was that the goal of tactical exercises for tactical skill is to learn new patterns.  So set a time limit (like 5 minutes) and if you haven't solved it look at the solution.  After failing 5 or 10 stop and go over those failed puzzles until you can do them easily / blindfolded / whatever.  Learn a few new patterns each session and you're on your way.

I used to do them (without knowing it) for calculation/visualization practice.  I gave myself no time limit, and would not move the pieces or write anything until I was satisfied with my analysis.  Then I'd write all the variations I saw down, as far out as I thought they might require.  After 10 or so puzzles I'd check all my answers at once.  After about a month I found this really helped my OTB organization / analysis ability.  I found myself rarely needing to re-check a variation during play.  (I'm rusty now so I'm back to fumbling though multiple lines at once, re-checking as I go, with a final check at the end heh).