Cleaning my make up brushes is a task that I tend to put off doing, even though it's one of those things that really shouldn't be pushed to the bottom of the 'To Do' list. For me it's a lot of effort and it can be slightly inconvenient as I don't have many brushes but I use them all daily and after deep cleaning, the brushes need a day or two to dry, so it's hard to find a time to wash them when I won't be needing to use them the next day. Although it's something that has to be done as leaving them unwashed allows old make up, dirt, oils and bacteria to build up in the bristles, so continuously using them without giving them a good clean spreads the dirt around your face which lead to breakouts (which I don't think anybody's a fan of!).
I usually spot clean my brushes using the MAC Brush Cleanser from a daily to weekly basis depending on how often I use the brushes that week or which brush it is. I tend to spot clean my eye and foundation brushes on more of a daily basis because I find they get the most dirty. However I deep clean all my brushes around every two to three weeks, even though I should probably do it more frequently I am just very lazy.
For deep cleaning I use Johnson's Baby Shampoo which I really like as it leaves my brushes soft and clean, it was also recommended to me by a make up artist so it must be alright! Other alternatives to mild shampoos are brush cleaners or hand soaps, these are gentle so won't damage the bristles.
This is the routine I stick to:
Run warm water over the bristles with the brush facing downwards to make sure the water doesn't run into the ferrule.
Put a little bit of shampoo/hand soap/cleaner into your hand and swirl the brush around to lather up the product.
Keep repeating until there is no make up left on the brush.
I leave my brushes to dry either lying down on a towel or placing them with the bristles over the edge of a surface to help the brushes keep their shape. Although I never dry them with the bristles facing upwards, as it can cause the water to run down into the ferrule and eventually dissolve the glue holding the bristles together. Brushes can be so expensive and after I've invested in one I really don't want it to be ruined within a few years.
Hope this was slightly helpful!