An extremely overlooked trick when programming synth sounds is using the key velocity or note position to modulate parameters. What I mean by this, is controlling certain features and controls in the synth by hitting the notes at varying levels of hardness, or their position on the keyboard. The simplest application of this is by setting the volume of the synth notes to correlate with how hard you hit the key, with the hardest note hits equalling the loudest resulting sound. Many synths offer more than this however and it can lead to interesting results.
After playing around with just the volume of the sound (which many synths are set to automatically respond to), we can look at other parameters, or settings to control. One of the simplest is the filter cutoff. By setting the note velocity to modulate the low-pass filter cut-off, harder key hits can result in brighter, or duller sounds. This can be great for when you are synthesising guitar like sounds where you want to mimic the brightness of a harder picked note.
By modulating the filter with the note position, you can allow the higher frequency notes to be at a different filter cutoff than the lower frequency notes. Some synths like Serum offer deeper control where you are able to modify the linearity of the effect.
Another great parameter to modulate is the LFO rate, where harder hit notes result in faster, or slower oscillations. This can be ideal for dubstep wobbles where you don't want to automate the rates after laying them, or don't have a modulation wheel.
Alternately, you could set the LFO rate modulation to note position, meaning the lower notes wobble at a different rate to the higher notes. By adjusting the curve you can set all the bass notes to wobble and set the LFO rate to zero with the higher notes so they don't wobble at all.
If you have a wavetable synth, you can modulate the wave position to have constantly changing sounds as you hit each key, which can generate very complex synth lines for little more effort than setting it up and playing around.
Furthermore, you could modulate the in built-effects Dry/Wet controls to change with the different intensity hits. A great one to try is reverb, where the hardest hits, or highest notes, are much more reverberant than the soft ones.
Finally, one of the coolest parameters to modulate is the envelope attack. This can be create for string sounds and pads where you set a long attack for the soft notes, and a fast, pluck-like attack for the harder hits. This can essentially make your patch a pad/lead hybrid, controlled by the velocity of the notes you play.
By combining several, or all of these modulations you can vastly expand the amount of expression and control which your patches have, literally at the touch of a key.