What should I pay attention to before buying a laptop? Any suggestions for the brand, CPU, video card and any other hardware stuff?
Not really... You get what you pay for. The more you spend, the better it will be. If you're not going to be playing a lot of 3D games, I'd recommend getting a cheap one.
Not necessarily true, although it generally is... You often pay a premium for Mac laptops simply because its Apple, whereas you could have purchased a superior Windows laptop for a fraction of the price... It would depend on your budget obviously.. but I would be looking for an Intel CPU, preferably an i7 however whatever rocks your boat . Some form of nVidia graphics card, a nice amount of RAM 8-16 GB should be ample for most things (I went overboard on my main system with 64GB of RAM and I never use more than 10 GB lol). Also look for 2 HDD's if you can, an SSD for your Windows installation and another HDD for your documents/media/games etc... Hope that helped.
In addition to reading all you can, it would be nice to go to Costco, Walmart, Best Buy, etc. to get some hands-on experience. I would also buy from someone who accepts a 30 day return with no restocking charge, in case it turns out to be one of those "I'm sorry, the laptop works but I'm just not happy with it." situations.
If $$$ are a serious issue, you may want to consider a used (or refurb) laptop. I've bought a couple on eBay that have been great. eBay - buy only from sellers with a high (+99.5%) rating and use PayPal for protection. I suggest an Intel Core2Duo cpu as a minimum and a dedicated video (usually nvidea) card. Another plus is that older laptops are going to have years worth of history on their performance, so it's more likey you can avoid the real dogs.
If you live in the US, back to school, and Labor Day sales abound. Also, if you live near a Micro Center, check them out as well.