Welding Tips and Tricks

I have collected a bin of scrap steel to use for practicing. Unfortunately I keep the bin in the garage and even the cold rolled bits have surface rust and there is still mill scale on other pieces. What are some good ways to prepare the surface for welding?
Most pieces a kind of small to hit with a grinder. I usually use a Dremel but it takes quite a bit of time. Would a vibratory tumbler get the surface clean enough?
Thanks for the help in advance.

For TIG, you want them as clean as possible. I use a flap when on my 4 1/2 grinder, and I usually clamp them down with a C clamp. A tumbler might work, but if they are so small you can't hit them with a grinder, I don't know how much practice you can actually get with them.

I'd let them soak in a container of naval jelly.
Muriatic acid would also work but it really accelerates future rusting and it's dangerous. Do the whole glove and eye protection thing and either wear the right vapor mask or make sure the wind's blowing away from you.
If you were doing this on something you cared about and couldn't use a flap wheel, there's products like Picklex that are really expensive but work well.

A bench grinder with a wire wheel on it will get the job done right quick. Use a face shield though.