At this point the goal in arena and coliseum might be to make challenger level. If you are already there then it might be to place well each week. Fun fact: there is always someone stronger, but you don’t have to lose to them. This is where CW comes in handy. You can figure out synergies in your teams doing CW.
Campaign is straight forward. Build up your heroes. Stars, levels, then mods. Also be sure to add in any friend memories when strong enough. If you are on a newer server you should make it through without mods.
You are going to need gold and diamonds. So, you need to work out a plan and stick to it. Some players never refresh their stamina beyond the 50 diamond level. Some never buy chips with diamonds. Some people sell badges, XP, red skill and hero chips for gold. It all depends on your priorities. Running low in either one limits your ability to move ahead when needed.
At your level you should have figured out that you probably won’t level up every hero. Pick the core group you like and keep them leveled up. Next you might pick heroes you use often enough as alternatives. Keep them within a reasonable distance so that you could level them up within a few days. There are others you need for friendship battles but little else. Do the minimum until they become important to you.
Use your guild to help in every way. Make sure you return the favor. Ask for stamina daily. You have two opportunities to request adding a skill level each day. Work together in Invasion to get those free mods. Borrow a mercenary for battles in Surge and CW often, and post your heroes so you get rewards too.