Clean, dry roads represent little hazard to the cyclist, but prolonged rain can turn a normally manageable surface into something far more challenging. Puddles, water filled pot holes, leaf litter and other debris can bring you down. The simplest and most effective tactic is to avoid them. The temptation to ride through puddles should be avoided at all costs. You’re unlikely to have any idea of how deep they are, or what lurks within.
Surface hazards are not only limited to seasonal debris. Perfectly legitimate features such as white lines can become treacherous. Where a white line is impossible to avoid, perhaps a chevron marking a tight corner, reduce speed in advance of the hazard, braking while on an unpainted section of tarmac. Do not under any circumstances brake while on the painted surface. The same applies to drain covers, yellow lines and their ilk.
Steering on suffices like painted lines and manhole covers can also be dangerous in wet conditions. If they cannot be avoided, try to approach them straight on, and in an upright position, rather than the leaning. This requires caution and awareness of surrounding traffic.