The method here is for rollers but the principle applies to brushes too. Take your time and look forward to the end. If you use cheap brushes and rollers it's a total waste of time. Invest in high quality equipment and look after it - stop work at LEAST half an hour before the end of the working day and look after your tools properly. This means cleaning them, maintaining them and putting them away lovingly for the next session. IF you don't get the paint out altogether, completely, you'll never get a good finish with a brush or roller ever again. Bear this in mind before embarking on the voyage of cleanse. And you should only really do this with high quality, which generally means expensive, brushes or rollers that can take the wear and tear. And do not for a moment even think of bothering to do this if your roller sleeve is a sponge. It has to be the furry type for this to work. You needs lots of warm water and soap. Patience, elbow grease and determination. Being OCDC may be a help.
Wearing rubber gloves, squeeze as much excess paint out of the roller as you can. Put a lot of effort in here. The more you get out now the less you have to work for the rest of the process. Squeeze the paint into kitchen roll / newspaper and put that in the bin. You might be breaking environmental laws here. When the roller's as dry as you can get it - at this stage it will look like the fur of a bald drowned yellow cat - immerse it in warm water, squeeze the roller repeatedly in the water and wring out as much paint as you can. Do this again and again, your wrists and fingers will ache. You will splash dilute paint all over the back of the sink and likely splash the floor, your clothing and shoes, and probably get some in your eyes - rinse them thoroughly in clean water if you do. When the water's taking no more paint, as in the water's got so much paint in it you can't get the roller any cleaner, empty the sink and start again. When you think you can get no more paint out, ever, squeeze out the roller as dry as you can then squirt liquid soap, washing up liquid is good, up and down two sides. Rub the soap in as evenly as you can all around the roller then wonder at all the amount paint that comes out of the roller's deep pile, which you thought you'd cleaned thoroughly... Do this again and again and again and be amazed at how this process impacts on the environment. Keep going; it takes ages. You will probably break sweat if you're doing it right. When there's no paint coming into the water - the water remains clear - repeat with liquid hand soap with skin softener to condition the roller for the next time you use it.
Or chuck it out and get a new roller the next time you need one.
If you plan to be painting the next day, with the same colour paint, wrap the roller tightly in cling film - make sure NO AIR can get to it and even put it in a carrier bag and seal with an elastic band.
Good luck. By the way spend time picking off all the paint from the roller handle. Work clean.
And remember, if there's any water left in the roller the next time you paint. You will have problems getting an even finish.