What is the best way to rank up in arena?
Win.
But really, get a squad you click with and communicate your way to wins
If you are talking your CSR definitely get a team together or regular players to communicate with to get the wins racked up.
If you are talking just your SR play whatever playlist is featured as it pays out more xp. If nothing is featured they say infection pays out good xp for time spent in games.
Use your RP and be XP boosts every game. Stick to the features playlist (gold star games). Save your RP for when there are Platinum packs in the store, and then get as many as you can. Group up with others whenever possible as it increases your chances at winning. Don’t neglect assists. Throw a shot at every enemy your teammates are attacking. Good luck.