I got my self to 1000 rating pretty easily, even with quite a few losses you pretty much only move up in the lower ratings. I would have to lose nearly 40 games for every win to lose points. On sundays in ruin it seems like if you wait till later in the evening you get all the easy teams scrambling for their 10 games. My rule of thumb for meaningful progression while running without an assistant healer is if the queue is more than 5min drop it and run a different day.
In the arena, blow up the first target that can't go immune, 5v4 is easier. Think locks, hunters, shamans, and DKs. Dont hit warriors until you know they aren't gonna spell reflect. Mages will usually blow their block and give you 10 secs of free whacking on someone else the first time you throw flameshock on them. Not sure what the hell it is with priests but they seem to have a talent that makes them immune to being 1 shot, if they are healing just DoT them and purge off the buffs, it'll get them to refocus their attention.