The GPU is the most important thing but here's some basic specs:
1) best GPU
2) 6GB DDR3 system memory or higher
3) 1600x900 screen res or higher
4) Quality (good customer feedback)
5) SSD? Recommend hard drive as SSD will add to price and probably lower GPU quality. If SSD I'd get a 250GB model but again I'd probably get an HDD and buy your own SSD later if you want (and clone).
I've seen SSD's for as cheap as $80USD which are 250GB so maybe switch later if you get the free upgrade to Windows 10. It's hard to get info but it's nice to find laptops with TWO 2.5" bays. Unfortunately seems to be rare. (for backup. use HDD as 2nd drive if upgrade to SSD)
EXAMPLE...