Two ways to help get rust off your pan. One is to pour Coca Cola on it while scrubbing and the other is to scrub with salt. You have to re-season your pan once you do this. There is plenty of good advice and "How To's" on Youtube that will help you. Never use soap and once you clean any cast iron, always dry it thoroughly and set it on the burner a minute or two to help dry it out. Use a little oil when you do this.
Use the course sea salt you can buy it at Sam's, Costco or Walmart you may even be able to get it at Smart and Final. I use sea salt for cleaning my coffee pots, glass pans and it is great with cast iron. Like Bones said, never use soap on your cast iron and dry it really well and never let it air dry.
my policy is this: Clean the rust off with water and a clean rag, put the pan on the heat, put the food in...cook the food. Eat the food. Clean the pan with water, heat to dry, oil liberally inside and out. I use my cast iron for camping and it gets a touch of rust only if I neglect to wash/dry/oil it immediately after use. I usually reseason it just by cooking bacon and sausage in it first the next time I use it. Never any sticking problems with any of my pans.