MacBook Battery Question

Hey guys, I've done a lot of research about MacBook battery health but I haven't totally gotten the answer I'm looking for.

I have 13" MacBook 2010 unibody that I've been using since Christmas of 2010, so almost a year. Coconut batter is telling me I had 5770mAh design capacity, and it's currently at 4735mAh--82%. I have 258 charge cycles so far. My first question is, is this normal to already be down to 82% not even a year old? Have I possibly abused my battery in some way? (p.s. I have done calibrations a couple times and haven't noticed any difference one way or the other). FYI, my Mac stays plugged in a great majority of the time, in my room temperature house.

My second question is, is there a way to increase my current 82% capacity to perhaps 88-90% or is there no coming back from capacity decrease? Is there something I can do going forward to preserve my battery? I plan on owning this computer for as long as possible, so I'd like to know if there's a way to keep it as healthy as possible. Thanks.