Permethrin treated clothing is the best deterrent I've used. Deet doesn't do much in my experience but if ticks get on pants treated with permethrin they get off as quick as they can. I've use this spray to treat my clothing before going out in the woods anymore: http://www.rei.com/product/768970/sawyer-permethrin-pump-spr...

One thing to be very, very careful of with permethrin-treated clothing is that it's very water-soluble, and extremely toxic to fish. If you go swimming while wearing permethrin-treated clothing, you will leave a trail of death in your wake, and not just of the bugs you were hoping to kill...

I feel compelled to note that it's also quite toxic to cats (but not dogs). This is one reason you should never use flea products intended for dogs on your cat.

Something with lots of DEET is the most proven way, though there are a lot of possible issues with that, and if you're going off trail a lot you probably can't beat the "deep woods" brands that are something like 25%.

An alternative is Avon Skin So Soft. Theres a good bet you'll hate the smell, and it has shown to be less effective than DEET but seems to be regarded as completely safe. But, to me I feel like I've always had better results for repelling gnats/flys using it over DEET based sprays.

Long sleeves, pants, and blousing pants into boots. Also, hat with wide brim. (and, personally, shaving my head, but that might be excessive).

My clothing is treated with Permethrin (it's standard for military uniforms, and available for outdoor clothing as a cream or spray). You have to be a little careful with laundering (avoiding dry cleaning).

DEET (and sunscreen) for skin and near edges of clothing.