I need to oil and clean my guitar fretboard and was wondering if a damp cloth and olive oil is good for this?
Short answer: no. As a non-drying vegetable oil, it will eventually become rancid and not be fun. Same as safflower, peanut, sunflower, coconut, palm, etc.
A better choice is a "drying oil" such as linseed oil, walnut oil, or a non-organic mineral oil or tung oil.
Some folks have had good results using a citrus oil (orange, lemon) to clean, and then an application of mineral oil to condition.
Olive oil, or any other vegetable-based oil, is not recommended for oiling any wood as it may go bad, or rancid, after a while. Most commercially available fretboard oils use mineral oil as their main ingredient. Mineral oil is inexpensive, will not go bad, and is readily available at most pharmacies. So if you want a cheap and virtually identical alternative to commercial fretboard oil, try using mineral oil instead of olive oil.
It's best to just wipe down your fret board with a damp clean cotton cloth. This is what Martin Guitars recommends for cleaning the fret boards of their acoustic guitars and it does work.
Lemon oil. I've used it for decades. Use it undiluted, and sparingly. I find it to be an excellent cleaner for unfinished fretboards. I generally use a different cleaner for the finished wood surfaces.