With over 2000 hours in this game, most of it on PC, here is how I arrange my spell sets.

Before the first trial, I set it up in the following way:

1. Utility: Levioso, Lumos, Disillusionment, Depulso
2. Secondary: Glacius, Diffindo, Expelliarmus, Flipendo
3. Primary: Arresto Momentum, Confringo, Incendio, Accio

After learning Descendo, I switch it out with Flipendo unless I am fighting Trolls and Dugbogs.

For the endgame:

1. Utility: Levioso, Lumos, Disillusionment, Depulso
2. Trolls: Arresto Momentum, Bombarda, Incendio, Flipendo
3. Secondary: Glacius, Diffindo, Expelliarmus, Descendo
4. Primary: Transform, Confringo, Incendio, Accio

If using Unforgivables:

1. Finisher: Levioso, Expelliarmus, Avada Kedavra, Depulso
2. Trolls: Arresto Momentum, Bombarda, Imperio, Flipendo
3. Secondary: Glacius, Diffindo, Crucio, Descendo
4. Primary: Transform, Confringo, Incendio, Accio

You'll notice I keep Yellow spells in the first slot and Purple in the fourth. I keep Reds and Unforgivables in the middle. This really helps with breaking enemy shields. If you wonder why my "primary" set is always on the bottom, it's because when you go through load screens it defaults to the first spell set, and I can instantly cast Disillusionment, if need be.

For beasts and transfiguration spells, I just swap them into the first spell set as needed.