Keeping your aligners clean is imperative to keeping your breath fresh. On a day to day basis I clean my aligners with a toothbrush and toothpaste. Once I have finished cleaning my teeth, I use the left over residue to clean my aligners gently, or add some more toothpaste if there is not much left. Although this does a good job of freshening them up a little, after a few days you will notice your aligners are not as bright, and to be quite frank, they begin to smell.
Therefore, once or twice a week, I like to use denture cleaners. Now, Invisalign do not recommend this, therefore do so at your own risk. However I have done this since the beginning and have had absolutely no issues in doing so. I have been using Steradent, which is available to buy from all supermarkets, including Boots and Superdrug, for around £1. It is very simple to use, just put one tablet into a tumbler, add your aligners and some warm water. Do NOT use hot water, as you do not want your aligners to warp - I just run the hot tap, and add the water whilst its warm. Leave for 10-15 minutes, rinse with cold water and you are done. It kills 99.9% of bacteria, leaving your aligners nice, clean and fresh.
If you have any tips, please do let me know!