I rather enjoy ballasting. In addition to the good pointers above I might add:
If you are using cork roadbed be sure the shoulders are smoothed out where the beveled cut is made. Sometimes there is a little ridge left there.
Vacuum the area well then the next step I do like Derek mentions above, is to use your adhesive, white glue, matte medium or my favorite, Mod-Podge, and I brush it on, undiluted (or very slightly thinned), the beveled edge of the cork then lightly sprinkle the ballast over the glue. At this stage the only IPA I’m using is in a chilled mug.
I let this dry over night, I don’t see any reason to vacuum the excess up since I’m going to be adding to it, then continue to apply my ballast between the ties and level it out. The previous application to the shoulders really helps keep the ballast from spilling down the shoulder and, to me, makes for a better contour.
LESS is better when applying the stone. You can always fill in a little more a day, week or month later but it is very difficult to remove once set.
Just before misting I use a small block of wood to tap the rail to allow the ballast to settle in and make sure there is none stuck to the rails.
I use a vee shaped device called a sampling spatula that makes precise application easier.

(The two tools in the foreground) also, your misting sprayer should provide a very fine mist so as not to disturb the stone, then SOAK the area generously.
Slowly apply your diluted adhesive of choice. I mainly dribble it along the sides of the rails so as not to disturb the ballast and allow capillary action to spread it.
The other thing that I believe makes for a better looking result is to use real stone ballast. I have never had good results with the Woodland Scenics brand.
Once everything looks good and is completely dr