I also usually set up various plotpoints and tropes that I want to happen.. .no matter if I will actualy use them later or if they are chronologically.
so I will think for example
"I want chara x.y. to be facing his phobia alone and freak out"
"I want to talk about this and that issue by having my chara meet this or that person"
"I want him to fail at this or that to give him a set back in his character development"
I also try to think ahead how my chara should be at the start and how I want him to change throughout the series... will they get more bitter? happy? does a charactertrait worsen?
it also helps me to set up stages of the comic ..
like in stage one character finds out about a scary truth/power and has to struggle to accept it
in stage two chara has accepted it and is working on improving the situation/hone his power
in stage three he is using that for his own advantage unti he finds out a even bigger thing that changes his opinions around
last stage chara has matured and sees his own mistakes and takes a different and proper route to make it right and better than before
there's a lot of approaches possible, just find the one(s) that suit you most
but if you are stuck after the start... try and take a big step back and don't do a tiny scene after the other, but wor on the very big picture
try and figure out the three or five biggest steps in your story, and then go from there
this will most likely lead to an arc structure.. but those can be pretty great for longe running stories