others will give advice which stuff is best for protection, but one basic rule.
Do NOT use washing-up liquid to wash the bike, we've discussed it before but basically it contains salts and stuff that just make corrosion worse.
Use a decent car body shampoo from your favourite accessory store. My preference is for Autoglym Bodywork Shampoo, but most are fine.
Also the Autoglym Vinyl&Rubber Care stuff is good for plastics and spraying onto just washed engines etc (it recommends it on the bottle).
If you want heavy duty protection
then Waxoyl does the trick, but it looks grubby. It's quite easily cleaned off in Spring with a spray of WD40 and a rag.