There's a hundred and one ways to keep you oil paint brushes clean, and everybody seems to do it slightly differently, so here's how I do it!
Some days, if I know that I'm going to be painting again the following day, I don't clean them at all. I leave them dipped in linseed or walnut oil which coats the oil paint and appears to slow the oxidation (oxidation is what happens to oil paint as opposed to drying - I'll do another post on this). Rembrandt did this using a tray that you can see in the studio display in The Rembrandt House Museum.
Here's some images I sent to a youngster experimenting with oil paint who was using White Spirit to wash their brushes all day:
