Robyn's answer gives some great strategies for working with a tutor online! Tutors serve a variety of purposes, so you can see them even if you are feeling successful with your work. I work with writing tutors specifically, and my tutors have a few pieces of advice regardless of whether the session occurs online or face-to-face.
First, remember that you can work with a tutor even before you start your assignment! They are great for helping you brainstorm for essays or talk through ideas before you put words on the page. Tutors can help you to figure out what your teacher is asking in the assignment, which will help you to avoid mistakes, or to help you figure out what clarification you need to get from a professor before moving forward. Getting an outline, thesis, or sources together with the support of a tutor might actually make the process of doing your work faster in the end.
Second, remember that a writing tutor isn't there to fix grammatical mistakes or correct your work. They're there to help you improve the argument, content, or evidence that you're using, so expect to see "global" comments (written comments at the end of the paper, but not lots of marks in the essay itself). Don't get frustrated if a tutor refuses to help with correcting - they are usually trained not to provide that kind of support. If you are worried about your grammar, the tutor will generally ask you to read your work out loud. You'll be amazed at how many mistakes you find!
Third, make appointments early! Tutoring services get bogged down at midterms and finals, so don't expect to be able to make an appointment with a tutor at the last minute, even online. Front load your appointments in the term to be sure you get help before the mad rush at the end of the term.
Tutors are a fantastic service, especially if you are using them in an online capacity.