Hello Jane! Always ensure that you have plenty of clean water. If you're painting in Watercolours, have two pots or tubs of water; one to clean the brush after each colour use, then swill again in the clean water. Keep your brushes in a stiff tube or wrap, ensuring that the bristles are kept straight, to a good point, if they are round.
For Acrylics, the same applies as above, but even more so, as once acrylics have dried on a brush then its very difficult, if not impossible, to get the brush usable again for good work. Same applies here for storage.
If you are using Masking Fluid, then rub a little soap into the bristles of an old brush before you use the Masking Fluid, then after you have finished with it, the brush will wash out much easier, as the masking fluid is washed away with the soap. Alternativley, use the SAA brushes specifically made for Masking Fluid, together with the pen for very fine work.
Just in case you are thinking about Oils, use something like Sansodor (Low Odour Thinners) to clean the brushes after wiping them first on a suitable rag.
If I've left anything out, or you want more information, then come back to me and I'll help as much as possible.
Good luck, good painting and very best wishes,
RSC Wigan / Warrington area