Im studying my level 3 hairdressing but haven't been taught this. I know that I have too use a colour eraser first and then bleach my hair. Im just wondering whether I have to do anything between bleaching it and putting the colour on?

Once you've done the processes you've mentioned; use a toner to get an even colour, condition well with a leave in conditioner maybe two times a week if your hair becomes the slightest bit damaged and then apply your colour.