New Stem and tips?

I just fitted a nice new stem to my bike as i have long arms relative to a quite short body, it made a huge difference on my little two minute test ride. However are there differences i should be aware of foor lenthier riding is it going to affect my steering a little?

Also i'm still relatively new to mtb-ing and would appreciate ay tips re trail riding and getting up those hills and then haring down them again.

A shorter stem will make for easier climbing and crisper turning. The degree rise of the stem will have an impact on your back and neck. If you have riser bars, they can be angled back a bit, and your saddle can be pushed forward or backwards also. All these things can make a difference on your ride quality. Hope this helps. :)