I find that the best approach for me has been a combination of discipline, proper breaks, and review. Setting up a time and a space for art really helps me find my groove when it comes time to draw, but moreover, forces me to work on a regular interval.
The other thing I've found helpful for the issue of "my art looks terrible" is doing something about it. Not in the "get over it" sense, but in the sense of self-critique and red-lining. If I draw something that I look at and go "That's awful!" my next step is to ask myself "why?" I then sit down and do a full critique and red-line of my work, asking what worked, what didn't, and tracing in what I think might have made it better.
Equally important is that you need to treat self-critique just like you would when critiquing someone else's work. You wouldn't (I hope) write "It's horrible and you're horrible and you should never draw again" when critiquing someone else's work because it would hurt their feelings and provide no useful feedback. Turns out, you can hurt your own feelings and make the problem worse. Instead, put a genuine eye to the work and try and apply everything you know about both art and critique to the process. Write in things like "This arc seems a bit ragged" and "I like the way the muzzle is shaped here".
When you finish, you'll not only know what's wrong with the work, but also what's right. And moreover, you'll have some insight into what makes the parts that are wrong... well... wrong, rather than just a vague feeling that you've done a terrible job. With a tangible sense of why you feel that, it's a lot easier to see what the next step is, and get pumped about doing it differently in the next one.