Hi,
I am currently in my third year or uni doing a full time work and have worked an average of around 20 hours a week. Although my circumstances are in the reverse of yours, I can relate to needing help with your question.
I found that i have had to schedule everything into my google calendar, to try and keep on top of things. Work, study time, assignments and exams due, appointments and I used different colours for each thing. Most importantly make sure you remember to make time for you and have fun too.
I find that a little bit of time spent on planning makes things much easier in the long run.
I hope this helps.
-Victoria
Wrexham Uni Rep