What is essential is to start with a list of the important ideas you want to put across with your branding, then the next step would be to create shorter version of these ideas completely independent of each other.
For example, if one of the things you need people to know is that you shouldn’t store the product outside, whilst exposed to the elements you would then need to think about the absolute shortest way that you can say it. It may be that something is quite important that, you will still need 15-20 words to say it. In that case then so be it, but if you can still meaningfully reduce the amount of words down to 10, that can still be great. Five words would be a bonus.
Having worked this out for all the different ideas, the final step involves bringing all these distilled essential information tit bits together into what will eventually form your product label. What other people don’t often appreciate is that white space is a powerful tool especially when used properly. Spacing out your information, instead of grouping everything together can make for a product label that has lovely easy to follow content.