My biggest suggestion is to keep practicing and don't start posting until you feel confident with your work. I know there might be a pressure to make a webcomic right away but if you feel like you still need to improve your craft before you start posting, that is OK.
I will also suggest that before posting, you should create about 10 to 15 pages before posting the first page. I notice some newbies will start posting right away than get burnt out after the 3rd or 4th page because they got a bit overwhelmed.
I will also suggest starting with shorter stories before taking on long epics.