Try doubling up sounds you want to give a sense of stereo to. For example, say you had a synth chord or something, bounce it out and load in a sampler, pan it L or R at a maximum of 3 or 9 o'clock, then duplicate the zone and on the new zone pan it in the opposite direction and detune it against the first zone.
The detuning really sets it off and gives a kind of wide stereo feel, just control the amount by using the 2 zones pan amount and fine tuning.
If it's a low frequency sound like a bass, keep the weight in mono by duplicating the zone a 3rd time and keeping this in the centre. Then change the left and right panned versions filter to HP and set a cut off point above at least 250hz.
You can also bounce out parts and add a small amount of millisecond silence to either the L or R channel of a stereo file. This causes offset which the ears perceives as a stereo sound too.
Being subtle is the key though, keep the weight of the track in mono and I find judging panning through headphones a big help as it tends to sound exaggerated as you aren't getting overflow, this helps to ensure you don't go overboard.
This is a handy tool:
Got it recommended to me when I was doing breakbeat, neat plug to use on busses.