Carrot & Stick
Finishing a comics page is of course its own delightful reward, but if you are having trouble sitting down and doing the work, it may help to use extra incentives.
I decided the other day to tie my comics-buying budget to my comics production. For each page I finish, I set aside a little money (amount varies depending on page size & etc.). I am only allowing myself to buy comics with this set-aside money, so if I don't make comics, I don't get to buy comics. You can pick arbitrary amounts like $2 for a mini-page & $4 for digest-size, or set your rates with unnecessary formulas like I did. You can also adjust your rates to help set priorities (more $ for the non-paying piece you promised to someone for a deadline, etc).
I'm hoping this will also encourage me to budget better in general...