What acne face wash should i use, and how often should i use it?

Whatever works: This is a very individualized issue. Some do well with otc products like neutrogena acne wash, or proactive. Some need an antibacterial wash like benzaclim. You really need to try some products and find what works best for your skin. Avoid the temptation to overdry your skin. At 31 it doesn't seem like a big concern, but it's a good idea to maintain moisture to avoid premature wrinkling!