Arsenal failed to win the Premier League because they could not maintain their consistency. I think the reason is that they don't really have the proper preparation and they don't have a lot of options to rotate players, so fatigue and injury became a big problem for them. Besides that, Arsenal also don't really have a winning mentality, one important thing that their rival (Man City) has.
Arteta certainly wants to make Arsenal even better this season, but I think it won't be easy for Arsenal to become champions because apart from Man City, Liverpool and Man United will also have the same target.
Many times last season Arsenal came from behind to win their games. There were times when they were even two goals down yet they still found a way to win. Arsenal of last season had a winning mentality. They played each game like their lives depends on it till they started dropping points due to injury and fatigue.
If they succeed in getting quality players to add to their squad they would be a powerful force next season.
Only Man City and Liverpool are the threat Arsenal face next season. Arsenal and Newcastle will have a better season than Manchester United.