The type of shaving formula you choose — oil, cream, foam — is based on personal preference, but the important thing is you have one. You don't want to shave dry or wet without a barrier because it'll irritate the skin, so having one makes for a more comfortable shave.
For beginners, or if you want more of a guide to areas so you don't accidentally glide across the skin more times than you need to, an opaque formula like a cream or mousse might be best. I like the Sundae Cool Mint Foaming Body Wash (£13), which doubles as a moisturising body wash and a shaving foam. Just make sure whatever you use doesn't contain any harsh chemicals that could cause an adverse reaction.