Join missions with the needed heroes
Volunteer for as many missions as possible
fill a mission who's requirements aren't met
forget to claim your missions
Ghost Ops starts every Thursday at reset and is well worth the time you put.
assist allies
complete your own missions
volunteer on extra missions to get contribution medals for the alliance store
only start missions that have all the heroes you need, and feel free to kick anyone that isn't contributing to meeting your goals
starting without max participants doesn't hurt you, but give your Joes a chance to join if you have free seats
start them as soon as you can, once they are ready (and enable auto-start) so you aren't holding heroes hostage
ONLY assist on missions that either
a) you have at least one of the required heroes, or
b) have already met the requirements (this one is a great way to get shards for heroes you are working on)
Join as many as you can to max your alliance contribution medals (and use those to buy cool things in the alliance store)
Good notes:
most missions take about 30 minutes, so check back and claim your completed missions so you can join more (you must claim your own missions, and they can be looted until all participants claim them)
this is a HUGE boost for buying things in the alliance store, so take advantage.
Want a deeper dive? Take a look at this guide.