I run mech Sisters. They pretty much do just what you said, ride up, get out, Divine Guideance, pew pew, plus Flamers.
As has been said, they're pretty weak in
CC. Not terrible, but
def nothing special. As a result, you want to try to pick off isolated units and burn them down with a couple squads. I.e. destroy them in detail.
Exorcists are a must. You'd be fine with 3x, but might feel cheesy, or not want to deal with that many kits. In that case, a squad of Retributors with HBolters is nice.
A squad of Melta-Dominions in an Immolator is a good trick, but it tends to be very hit or miss. Still, worth having, since when they hit, they tend to get something very important (Land Raider, for example).
All squads want a Vet Superior for the Faith.
I gave my Vet Superiors trinkets like Power Weapons, Eviscerators, Plasma Pistols, etc. Probably not the best use of points, but if you're gonna drop something, I'd drop the Power Weapon first. A Plasma Pistol's firepower is welcome, when the whole gimmick of the list is to dump a ton of shooting in a short time.
Run up to the enemy, toast them, finish them in assault.
I think you'll find that you'd rather Rapid-Fire your Bolters than Assault.
The average Sister has a Bolter. She can shoot twice, or she can charge and attack twice. A Bolter is 2x BS4 shots at S4. Charging is 2x WS3 attacks at S3. Even with Celestians, who hit on a 3+, you're still only S3. The Bolter is AP5. Many units you might charge will have better than I3, meaning you'll lose attacks before they happen.
Shoot your guns. If one squad of Sisters can't shoot the the target down, bring two. Or support them with your ranged shooting (which will be rare).