When I play cash games, I find they are usually softer weekends and evenings, when there are more casual players online. No big surprise there.
In regard to MTTs, I have discovered in the last two or three months that it really helps my results to focus on one or two daily tournies and play those as often as possible.
Previously, I would just play whichever upcoming MTT looked attractive, and would flit from one site to another with no real plan.
Playing the same tourney regularly has allowed me to get really familiar with the structure and pace, and to build up a body of notes on the other regular players.
The last point is especially important. It isn`t until you start doing this that you realise just how often the same handful of names reach the late stages. These are the dangerous players, and it is a big help to know their styles in advance.
Since I have been doing this, my MTT results (which were not shabby before) have stepped up another level, and I am final tabling noticeably more often.