100% Strata 2 Goggles - Black Frame - Mirror Silver Lens - Motor Psycho Sport 

You can use them for MTB. I think they have lenses that have vents built into them.

I would use some clear ones and when you get really good at dirt bikes I would switch.

The Strata's are our number one selling goggles. Beginner or not I don't think it will make a difference. We are in Southern California so riding without a tinted lens would be crazy, it's way too bright in the open desert. I have no problem recommending these to beginners, thanks!