13" screen size is optimal. 11" might be a bit small for some. 15" could result in a bulky laptop that’s less portable.
Check if it has a 1080p resolution. Many laptops skimp out on resolution (most are 768p-900p) but, apart from inferior image quality, there is also less workspace for webpages and/or multi-tasking.
Make sure it has enough RAM. 2-4GB is fine for Androids, Chrome or a basic mobile version of Windows 10. But if you’re running Mac OSX or Windows 10 and expect a full computing experience, try to go for 8GB of RAM if you can.
Although HDD hard drives are cheaper, SSD solid state drives make the computer much faster overall. Find a 250 GB SSD if it’s going to be a main computer, but if this is just your ancillary portable computer, 120 GB can be fine.
This is completely subjective but a good keyboard and responsive trackpad make the experience much more pleasant.
Battery life matters to an extent. 3-4 is very iffy. You might get a 4 hr class in the summer or express semester. You might have two back to back classes. Or, on occasion, you may forget to charge it. 5-8 hours is ideal because it gives you that leeway. But beyond that, 9-12 hours is not really that important because you’re likely to have access to a charger at your house, dorm, cafe, library, etc.
I’d caution against a gaming laptop. Either they are very expensive or they sacrifice in something in order to get a powerful video card inside of it.