The tips and techniques for this are the same as dragging, except you would slide instrument in the opposite direction in time. Sometimes drummers will speed up or slow down the whole tempo of the song. The entire band follows these tempo changes. This can also be heard in progressive music, where new sections of a song may have an entirely different tempo. Changes to the entire tempo of the song require you to alter the tempo map in your sequence.
Most sequencers provide a way to alter the tempo, either gradually over time, or instantly.
Any more than a few beats and the change may stand out too much. The key to randomisation is to be subtle. Apply too much randomisation, and your track will sound sloppy and amateurish. I've noticed that randomising the track helps separate the individual drum sounds since less of them are occurring at the exact same time. This also seems to increase the stereo image of the drums as well.