Why do you use GIFP as your picture format? I'd use JPEG (.JPG) personally.
Judging from the image I would say you make the usual newbie mistakes. xD But no worries, everyone makes them. ^^
First of all you should be using the right resolution when making a webdesign. Think ahead, planning things out is half the design already done.
I'd recommend using 2000px for your width, the height doesn't really matter as that may vary according to the content you want to include in your website.
I tend to use 2000x2400 as my default.
As for your content area, I would never use anything bigger the 1000px.
Use guides to help you with the structure of your website, things need to have the correct spacing etc otherwise they will look off and that's not good.
Now for your actual website:
The header image looks a little squished. Did you use Free Transform and held SHIFT while resizing it? (assuming you did cut/resize it at all)
Could use some effects on the image, such as making another layer, setting it on overlay and try darkening a few parts etc, increasing contrast bla bla.
Right now it looks rather bland and I'm sure everyone knows that image anyways as it's quite common.
Your menu bar is very bland. Simple RGB color, no texture, no effects whatsoever.
But it's hard to use proper effects for newbies so I'm not blaming you. Try learning more about Bevel and Emboss. That comes in quite handy.
At least you thought about centering your menu text vertically and gave it the correct spacing, that's good.
I wouldn't use any outer glow on the Menu Text though ;)
Your body elements (content box, sidebar etc) look very bland too, like your menu box. Try working with textures or frames to differenciate it from your background.
Your text and icons are VERY big. Way too big I guess. I'd make them smaller.
Hope I could help you a little. ^^