It sounds like you might need to understand your favorite openings better, or, more fundamentally, find some favorite openings if you don't have any yet. By the time you get 8-10 moves into a standard opening, that opening should already be specifying your best attacking moves. For example, in the main line of the Najdorf Sicilian and the main line of the Pirc, White has the attacking move f4, sometimes followed by f5, or at least intending f5, as already part of the opening analysis. Unfortunately, opening books often don't tell you *why* you're supposed to make those book moves, but you can fill in that educational gap by going through professional games that used those openings, and noting which moves and attacks the winners used to win. In general, the way openings usually transition into the middle game is that after you (especially as White) have a solid center, then you start to *expand* your center by pushing it forward into the other's guy's side of the board, usually by advancing a center pawn like P-K5 or P-Q5, especially if it attacks one of your opponent's knights at B3. For kingside attacks, P-KB4 followed by P-KB5 (as in the Sicilian and Pirc examples I gave) is the standard attacking move, or if the center is locked up, then P-KB4 or P-QB4 are typically used.
Such "expand your center" attacks, despite being fairly mechnical, work surprisingly well. I suppose the reason they work so well is the same reason seizing the center works well: you first control the high ground, then you start to treat everything as high ground. You get greedy. Or another way to view it is that you're progressively restricting your opponent's mobility, which means he/she can't fight back as well, then after a certain point he/she can't defend adequately when you make an attacking thrust. By analogy, it's like backing someone into a corner, or like spraying someone with sticky material so he/she can't move as well to defend themselves. You wouldn't want to be defending yourself in a sword fight under such deteriorating conditions.
It seems to me that during the middle game, I am almost always playing defense. When I do try to take the initiative early, I quite frequently miss something and end up with a losing position. Is this a symptom of playing too timidly or could defense just be my natural style?
I know any input has to be general without analyzing a lot of games but I'm only looking for opinions from others who might be having the same experience.
Thanks.