Motivation is hard because it takes motivation to get started. When you're missing that it's tricky. For me, if I don't feel motivated, I try bribing myself with something. "If I do this, I'll let myself do something I really want to afterwards." Sometimes I find that getting started is the hard part. Once I'm studying, it's easier.
Another thing I do is take myself away from anything that could distract me. If I'm on my computer, or next to it, I'll start working but then 'I'll just check my emails', or 'I'll just check that website I wanted to look at.' Before I know it, I'm playing games and have done nothing at all. Make a space for yourself on the kitchen or dining room table, or find a corner in your bedroom or living room where you can sit and have nothing near you that might successfully distract you.
A third option is to find someone to partner with in your studies. Even if they're online. Challenge each other to do a set amount of work/studying in a week. Having someone to challenge can be very motivating. (Also, if your friend/study partner has done their work and you haven't, it can make you feel quite shame-faced and encourage you to do better in future!)