When to go for winners?
There are two times a player should go for the big winner, especially with a loop. The first is obviously off a weak ball that pops up, or often a lower ball that lands in the middle of the table (which is easy to loop kill). However, we all have seen top players rip winners off what seems to be effective low serves and pushes. Shouldn't we try to do that as well?
The key is whether you are both in position for the shot, and not only have read the ball's spin perfectly, but know you have read it perfectly. (Nobody really does anything "perfectly," but you get the idea.) Top players are almost always in position and almost always read the incoming ball, and so they can go for a big shot. (Plus, of course, they are top players, and so are skilled at making big shots.) If you have a good loop or smash, and are sure you have read the incoming ball very well, then you can go for the shot. This doesn't mean ripping it like the pros, but you can go for perhaps 80% power. That, and good placement, should generally be all that's needed to win the point. For most shots, if a little light bulb doesn't go off in your head that tells you that you have read the ball perfectly, then you probably should focus on aggressive, well-placed steadiness and save the winners for another shot.
Aggressive, well-placed steadiness
Think about it. Aggressive, well-placed steadiness, combined with opportunistic putaways, good serves, and good tactics - put these together, and you have quite a game. (I toyed with adding "controlled receive" here, but that really comes under the "aggressive, well-placed steadiness" banner. A well-controlled receive is actually aggressive as you aren't giving the opponent an easy shot to attack.)
Focus on basics