Like buying any major purchase, first think about what you intend to use your laptop for - if it's mostly surfing the net and email, you may want to consider getting a netbook. Reason, they are smaller and cheaper, and basically designed to be light-weight laptops.
If you have plans to do business or club stuff - and need things like a word processor or excel - then consider the laptop, but you may not need one of those suped-up versions. For those, do some comparison shopping online to find a brand that you'd feel comfortable with.
If you have plans to do video or picture editing or gaming - you'll want to look for how much RAM the laptop has. The more RAM, the better processing power the computer will have.
Other than that, consider how much space the laptop has (hard drive Gigs - or Terabyte) - if you are planning to download lots of videos or have lots of pictures, you'll want to get a laptop with more space. An alternative to make this cheaper is to consider getting a cheaper laptop with less space, and buy a separate external hard drive to extra space if this is something you need.
As far as brands, I tend to prefer Dell - that brand has always been very stable for my needs. HP is another quality brand I'd recommend. Also several of my friends own Sony Vio's and they are happy with those.
Good luck on your shopping!