Re: Oiling the Fretboard
This is very important in a high-end guitar, not nearly so much in a mass-produced import or the like.
Oiling preserves the wood, and permits it to age better and play easier over time. There are multiple types of oils for woodworking, and all have different purposes depending on their volatility and ‘drying rate’ - that is, how long it takes for certain oils to fully dry and/or absorb into the woods.
The most common oil for working on necks and other unfinished (non-lacquered) woods is tung oil, which can be found at most hardware stores.
I use a light furniture cleaning agent, like a few spritzes of Lemon Pledge on a soft rag for cleaning the finished surfaces.
For really bad areas, a couple drops of Murphy’s Oil Soap in warm water, then applied with a medium-soft rag does the trick.
I assume we’re talking acoustic here.
It is totally okay to change them all at once, and thus be able to effectively clean the fingerboard et al, IF you are staying with the same brand and gauge.
If you are changing gauges, have somebody who knows what they’re doing help you, as you’re most likely gonna need some truss rod adjustments afterward, to accomodate the differing tension on the neck. This is easy to do, though, and if somebody is really interested I’ll get into the whys and wherefores of tension adjustments on acoustics. But it’s detailed enough that I won’t go there unless somebody requests it.
if you are a regular player, you should change your strings probably monthly. I strongly recommend Musician’s Friend brand acoustic strings (at $2 or so a set for most acoustic gauges in 10 packs), and they are cheap enough to change weekly if you’re starting to play out. They’re pretty nice sounding, and last a bit.
Fresh strings will make a difference in your playing and your sound. Don’t waste your time on Elixirs unless you’re playing out more than 2-3 times a week. They’re not worth it.