The best tutorial's are life. I think you used the grass brush though and that's not to good of a thing to do. Look at some photo's and try to copy the grass look you want. I haven't seen many good tut's on grass and I think it's because it's so full of varaity for instance there's freshly mowed grass, the wild fields of ireland grass, grass under a tree and so on...

It look's like you spent a ton of time on the guy's face, then lost intrest around the background part. Next time I'd suggest using alot of reference photo's www.corbis.com is a good source and really look at lighting, how water reflects, how fabric drapes ect...

For a first...it looks pretty darn good. I would pay attention to the crit and suggestion kariefury gave, butalso look into some tutorial on color theory. You have some colors in there that are working against each other and its very distracting.

Stefan Cel Mare!