Also a huge proponent of Bounce - Hit.
Get your racket back when your opponent hits the ball then start your swing as soon as the ball bounces.
Taking small steps leading into swinging also helps with making minor adjustments to getting in proper position to hit the ball.
Like @mad dog1 said, a big first serve doesn't make you an aggressive player. I would consider serve and volleying an aggressive play style and doesn't require a big first serve (e.g. Rafter).
Aggressive play is more shot selection oriented than pace/power oriented imo.
Just timing and rhythm. You start your swing as soon as you finish your take back. Some people hold the racket back with their left hand while they are waiting to start their swing. You don't have that pause.