Focus on ships and arena for crystals. I personally can't compete in ships cause I'm f2p and in a very hard shard with whales. I don't see many f2p in top 20 of ships at all but it is possible if you are lucky with a good ship shard and start early farming the tie fighters for tarkin capital ship (easiest way to get a good offensive and defensive team due to the turn meter shenanigans they provide).
Make sure you farm the toons required for CLS. He is a must have now for all parts of the game.
I am one of the top f2p in game and in one of maybe three guilds in top 50ish that aren't part of a huge alliances or mega whale guild.
https://swgoh.gg/u/warmonkeyy/
Good luck! I guarantee you will be frustrated if you care about good arena ranks but that's part of the fun and how you know you care lol