need help (have never really repaired and painted before)

I have a brownstone (moneypit) and the upstairs windows have 2 ft. sills that need patched and painted. I sanded,wiped,spackled,sanded then painted but some of the paint is coming off already.

My question - to patch these sills do I need to apply --sand---primer----spackle----sand---primer---paint?

Is this the correct sequence to assure the paint sticks this time. Sorry I'm a nurse -can help with health questions but not any of this stuff. Have a subscription of the magazine and its a help and interesting.

Thanks for any response.

Katepalm

Is this for inside or outside?

If this is inside, scrape as much of the old paint off as you can, sand it with rough sandpaper, apply a light coat of spackle, block sand it smooth with fine sand paper, prime it once or twice, then give it a couple coats of top coat. Make sure everything is really dry before you begin each step. 

Good luck with your project!

Curt