Sketch out your layout ideas on paper or on the computer.
Even if it is messy.
Beginning Thoughts:
What size should I make design my page?
640 X 480 (600X300) dpi
is small
800 X 600 (760X420) dpi
is small
1024 X 768 (955X600) dpi is standard
The second size refers to your actual screen realestate, the area left over excluding your scroll bars and top navigation of your browser.
Sketches
Sketch out your layout ideas on paper or on the computer.
Even if it is messy.