This won't be cheap:  laptops used to cost many thousands of pounds (or dollars) but nowadays they can be had for a few hundred;  that's wonderful but they're still awfully expensive things to buy and even more awfully expeensive to get wrong.  Don't be pressured or jump into anything - unless you're *truly* desperate, your business is losing money or you're missing assignment deadlines taking a little time will REALLY pay off. 

Buy something you'll actually like:  Apple's marketing people used to say:

"The most powerful computer in the office
is the one that gets USED". 

If you like the laptop you buy you really ARE going to use it more – you'll get so much more out of it and your money is so much better spent.  

If you hate the keyboard, find the screen hard to read, find it too heavy or the battery doesn't last long enough - you really won't get as much use out of it.  You'll have wasted your money no matter how good a deal you manged to get.

Think like an accountant:  Break the purchase price down and think of how long you’re planning to have it for.  If you work out how much it will "cost" per day then you can think - is this really going to be worth $3 per day to me?  Is it worth £12 per day to me?  

Your budget will tell you how much you can spend - this will help tell you how much you SHOULD spend.

Think ahead - not backward:  If like me you don't have ready access to a time machine - you have to think of how you're going to be using it in 3 months time or 6 months or 18 months time.  If you think "oh 6 months ago I had to go to lectures all the time so portability is a big deal" - but now you will only use it at home - then battery life and mobility isn't as important.  

Be broader in your thinking too - Are you going to take it to work?  Use it on a train to watch movies, play games or browse Facebook?  Are you going to be using it in libraries and lecture halls or just at home?  Is it going to the cabin on the weekend with you or will it never leave the confines of the kitchen table?

Try them out - hands on is SO VERY IMPORTANT:  All laptops have aspects that you will love and loathe - there's no perfect machine out there;  some have bits you can live with, some bits you can't - and some bits you'll love.  

Go and look at them - try them out, get some hands-on time with them.  If you've done your research and find one that looks great on paper - but then you find it cheap, flimsy and with a bad keyboard - don't ignore this impression.  Remember - YOU'RE the one who has to live with what you buy - not the person you asked about it!