Originally posted by Montague
What Salmonbug said above...
Except: for a beginner on a grass field that is mowing grass with a 2.5" clearance, that tells me you have long grass. We've had a really wet spring out here this year, and the grass on the field is longer than anyone remembers, it's scary.
When the grass is long, a nose high attitude is best. You won't have the problems with bouncing in to the air on landings because the grass will cause so much drag on touchdown that you will "stick" quite well. And on takeoff, you need that nosewheel out of the grass as soon as you can, so ever bit of nose-up helps.
If you are flying from pavement, what Salmonbug said is right on.
I just went to a 2.75" wheel on my nosewheel on my extra trainer to make the plane sit nose-up for easier take offs in the high stuff. 3.5 is a bit big, but maybe not too big, depending on your field. I used to fly off of some really un-prepared fields, and we used 3" mains and 3.25 nose wheels on .40 size trainers, and frequently made our own heavier wire nose struts that were longer than stock to get more ground clearance and not bend so much when we hit the potholes. Had to really reinforce the gear mounts and firewalls too. Ahh, memories 
At least we didn't have to walk 15miles in the snow, barefoot, uphill both ways.
I don't pay the landscaping bills where I fly, so I do have to put up with real long grass at times. I'm going to try the "nose up" attitude with a bigger wheel up front.