Guys, no offence, but if you don't know, don't post.
APC is correct. WD40 and "some kind of solvent cleaner" is very wrong.
Kerry, as Pedro has posted, Meguirars APC (All Purpose Cleaner) liberally sprayed over the offending areas MAKING SURE THE ENGINE IS COLD. This can then be agitated to get rid of stubborn marks and dirt. Then sprayed with a lower pressure washer, again as posted by Pedro, using common sense. Some cover electrics, others don't but are careful not to aim the nozzle at particular areas.
Once finished, start the engine to aid drying. The plastics can then be dressed with something like Auto Glym Rubber and Vinyl dressing and metals polished. Paint work is treated in the same way as your bodywork, but sealed with a high temp sealent like Finish Kare 1000p.
Hope this helps.
Jamie