Many conciderations go into buying a laptop...
So here are a few handy tips to buying one:
1) Do you really need a big Hard Drive?
Usually... No... Mostly you will be storing videos/music/work stuff and maybe a game or two... About 130gb is a nice size, You don't want to pay too much for a lapop with a big HDD that you will never use up.
Screens are one of the main parts of the laptop... 15.4" may not seem like much but it will be massive... So don't go over the top if its for work... Gaming laptop's tend to have bigger screens for obvious reasons... Also, Smaller screens mean extra compact. So if you want something that isn't big, go for a smaller screen.
3) Graphics Card
Most of the time, Graphics cards in laptop's will not play games... So if you want games, Get a laptop that was built for gaming (Alienware / XPS) but if its for work, A good graphics card is not needed. Same goes for music and videos...
4) Built in stuff
Things like built in Webcams/microphone/face recognition may not be any use to you, So try to avoid them if you don't want them... They are often just a waste of money if you won't use them.
Thats basically all I can think of, Just shop around, Do your research and you should get the perfect laptop!