????????? Sterling silver may tarnish but it does not rust. Only iron rusts (http://en.wikipedia.org/wiki/Rust) and I've never heard of iron being used as the alloy portion of sterling silver.
Tarnish on sterling is caused by the copper portion. (Sterling silver is 92.5% silver and 7.5% something else - copper is usually the "something else"). If you have a lot of sulphur in your air (e.g. smog), you'll find it'll tarnish faster.
So, there are a couple of options here. First of all, you could work in fine silver (99% or more pure silver) which doesn't tarnish or you could try Argentium silver which does tarnish but [allegedly] at a much slower rate than sterling. The drawback with fine silver is that it's softer/weaker than sterling. Argentium silver is 92.5% pure silver just like sterling but the 7.5% portion is different (http://en.wikipedia.org/wiki/Argentium_sterling_silver). Argentium is more expensive than sterling. It's my understanding that Argentium reacts to heat a little differently than sterling, so if you solder your pieces, you'll need to research that a bit more.
If you decide to stick with sterling, then your pieces should be stored in airtight baggies when they're not being worn. Strangely enough, for most people, constantly worn items don't tarnish. I think it's something to do with the natural body oils forming a barrier between the silver and the air. Having said that, some people's unique body chemistry can react with sterling and those unfortunate souls end up with a lot more tarnish.
Even if a piece does tarnish, it's pretty easy to clean silver using a commercial cleaner/polish or the washing soda/aluminum method.
I have no idea what would cause gold to tarnish - I suspect that, as with sterling silver, it's actually the alloy that's the culprit, not the gold (which doesn't tarnish).