that depends on the niche of the website. in general you can look at similar websites and create your own design based on the requirements.
i just started as a hobby. a friend of mine had the program dreamweaver and i started messing around with it and now im hooked on web design. a year ago i started doing research and found out that you can make money in this. not only web design but having websites that can generate money by placing ads and selling ad space.
If I am designing a flash site I will look at: http://thefwa.com/ For design and HTML sites I will look at: abduzeedo.com psdtuts.com www.good-tutorials.com www.smashingmagazine.com Out of all of them I find the envato network (psdtuts, nettuts etc) the most useful. They have a premium section which costs about £5 per month. I am still unconvinced whether it is worth it given how much you get for free but I am still paying for it.
Before i start designing i usually visit first these websites: smashingmagazine.com and csslounge.com to get some idea or inspiration.
Browsing other sites in the same niche. Browsing similar sites in other niches. Turning on some good music. Firing up my computer and unleashing my ideas