Depends on the following...
...HOW bad does it look, what kind of shape is it in, HOW much time/effort do you want to put into it, and HOW long do you need it to last?I trust you're talking about the teak on the exterior. Here's some suggestions:Wipe off as much of the oil as possible; on top of Cetol (base or gloss) it's not doing the wood any good at all. It's just making a mess. Before I begin with Cetol instructions, please be aware of another product, Armada, that has the same general purpose but does not have the "orange" tint that many people find offensive or unsightly. I use the Cetol base and gloss for two reasons: 1) I can get it by the gallon a lot cheaper and I have four boats to keep up. 2) The Cetol Gloss overcoat has a UV protectant in it as well as staying just a wee bit soft; when you drop something on the handrail or teak, it dings the Cetol and not the wood. (If you've got two thin coats and one thicker one.) You can step all over it, drop stuff on it, run lines over it, scrub it, clean it, rain on it, hail on it, ridicule it, say mean, uncaring things to it, and it really doesn't care. Two years later, you just give a 4-6 minute smoothing over with sandpaper and apply one more thin coat of the gloss. After about 6-10 years, you will have to remove the teak and start over but you will have few or no dings and the wood remains healthy. The Armada looks better, but the gloss doesn't last as long and it's more expensive. The trade-off? You have to look at wood with a bit of an orange tint but you don't have to mess with it as often. I'm nearly blind anyway, and as long as the wood LOOKS like it's in good shape with a bright clean finish, I am not so particular about the shade of the finish. I'd be happy to show you pictures of a completed job if you like.If the current Cetol application also has the gloss on top and the wood doesn't look that bad, you can sand over the gloss with 150, then 220, then apply more gloss on top. I suggest you use two thin coats vs. a glob on the first pass.If the wood is good shape but the finish looks horrible, I suggest you remove the current finish. Quick way: Electric orbital sander to sand off old stuff with 150 then 180 to smooth, mask areas, apply 2-3 coats of base then two coats of gloss. Long way but better results: Remove teak, take home to the garage, completely strip/sand down to bare wood, three coats base, two coats gloss, reinstall. don't forget to put duct tape over the holes in the cabin when you remove the handrails/steps/whatever.If the wood is severely cracked, I suggest you start over with new teak. It all depends on what YOU want it to look like.