My 2 formations

At the start sorry for my english.
- arena is another 1 of the reasons, why it is important to raise lvl of heroes (to unlock their skills and to be able to do their Quests). For completing their Q u gain gems too.
- it is better to use heroes with countering skills (they can trigger several times) rather then 1 time skills (like before/during combat increase/decrease strength). Especially in positions 3,4,5 where they have enough opportunities to react to opponents skills
- sometimes it can be harder to get from 3000 to 3200 then from 3300 all the way up to 4500. In such cases i watch what formations i am standing most of time against and counter it. You could even play several friendly matches to check what kind of formations are around your rank/points and prepare your self

Arena Tiers 1-3:
- here cant be said much, set formation and try to go as high as possible
- it is good to know the skills of heroes to be able to anticipate what to expect and if you have the time to change your formation accordingly before every fight (this is more important as you raise above 3000 points)

Tier 4-5 battles
- above 3000, your formation will battle even when offline, so it is good to go to some standards that can win most of the time
- when above 3000, its important to try to reach 4000+ as fast as you can, at that point you will receive champion bags (50+ lvl items and quests items) and after month points are reseted back to 3000
- Before i was using loosing tactic: i changed formation. Used some idiotic one over night to loose points and after logging in in the morning i dropped (mostly by ca 180) so i was still above 4k but matches were easier

At the moment i just switch between 2 Formations:
1st:

against most common increasing strength formations (identified by louca or darthos last place, in 1 of first 3 positions is definitely fiora and oneira)
Kuro is countering Fiora,
kurul/Louca just decreases strength based on positions
Mojian decreases when allies lose (this one could be changed for something better, but i don't bother with it, performs ok)
Francesca & Nya counters increasing strength


2nd:

against any other formation (mostly opponents trying to decrease strength)
-1st place kurul with decreasing (when very weak opponent against him then Odette with decreasing skill after win, Kurul 2nd place)
-2nd place Louca (or Odette when against weaker opponent)
-3rd Moijan with decreasing skill when ally looses (could be changed when opponent has 1st 2 characters weak, but i don't bother - too lazy)
-4th Fiora with decreasing skill when ally looses
-5th Kuro with 50% chance of 75% decrease (Louca could be ok here too or some other one time decreasing hero, but again, it works for me and am lazy)