All the time I get asked by my students for help with buying a new computer. I have gone through this process myself a few times and feel that I can help. Here are a few things I consider....
Value: There are certain brands that you can pay a premium for (Alienware, Apple, Dell XPS, etc). It seems like right now, every manufacturer offers a "high end" line. Sometimes I think that this can be nice, but it is not always worth the money. I guess that if it lasts longer it may be worth it, but if not it may just be a nicer looking machine.
Specs: You really need to take a hard looks at the specs of what you are buying. In my opinion there are some no brainers. Try to get at least 4gb of ram, 8gb if you can. A big 1tb hard drive is nice, but if it is slower (5400rpm), that may not be what you want. You may want to look for a faster Solid State Drive and then consider buying an external hard drive or using cloud storage. Also consider what graphics card and processor you are getting. Some packages that you see at different stores can often come with something weak in these areas. If you want to do any serious multimedia editing or gaming on a laptop you really need to look for a dedicated graphics card (like the Nvidia M series). Sometimes the integrated Intel or AMD graphics are good enough, but I would really recommend checking benchmarks to see how they perform.
Apple: You definitely pay a premium for an Apple, but the quality is there. The displays are always sharp, the responsiveness of the keyboards are great, and I could go on. I would not recommend spending extra just to get a Mac, but if it is in your price point, I would consider it. If you want to do some basic video, sound, or photo editing, it comes with the iLife bundle.
Performance: Using sites like CPU Benchmark or Notebook Check can be great. Check your processor and graphics cards for performance benchmarks, and also take a look for price vs performance comparisons. Sometimes you may be surprised. I recently bought a laptop with a m3-6y30 Intel Processor. It would have been an expensive upgrade to go with an m5 processor ($300 to $500). Although in some areas there may have been a performance increase, I did not think that it warranted spending that much more money.
Discounts and Sales: You really need to keep an eye open for sales. It is not uncommon to see a Laptop discounted by 20% or more during a weekly sale. If you are a student, work for the government, or work in an educational facility; you can also get discounts from Apple, Microsoft, Dell, and others. You just need to access their "Education Store". Usually the discount is about 10%.
Warranties: Whenever I have bought something at one of the large electronics retailers, they are always trying to sell me an extended warranty. I try to avoid these as often they are excessively expensive and never get used. Sometimes I will purposely buy a product at Costco as their price usually includes an extended warranty. Similarly, most major credit cards will have an extended warranty that will apply to your purchase as long as you use the card.
I hope that this guide helps, I will try to keep updating it if I can.
NM