The only precaution I take is if I have an engine that has a control module or starter in the engine valley under the intake manifold. Water accumulates in there and kills electronics and starters very quickly. Other than that, individual coil packs do a great job sealing the plug tubes against moisture. Spray some wd 40 on your electrical connectors and gently hose the engine off.
I'd avoid using a high pressure washer -- that's just inviting problems.
