@LOUISE is right. I've been through this process trying to reactivate an old - and large: 90k subscribers - email list, so i'll give you some best practices from my personal experience.
First of all, you make sure that you are using duble opt-in that requires new subscribers to confirm their signup, so you know they want to receive emails from you. Double opt-in lists have better subscriber engagement levels over time. This means more opens and clicks, and fewer bounces and unsubscribes. Double opt-in also safeguards your account against malicious spambots and scammers.
Another method is to check your list and eliminate invalid emails. There are many free and paid softwares and platforms that can do this for you, but i don’t recommend using free ones because are not 100% accurate and are less well developed (in terms of API) then paid services.
I’m currently using zerobounce (the 150$ package for 100k emails), and i think it’s worth the money invested. It’s very simply to use and provides a lot information about my campaign.
With this platform you can remove invalid emails from your list to prevent email bounces from ruining your delivrability, remove known email complainers and spam traps from your list, and append missing data (like location, gender, etc..).
If you want to test zerobounce, you can get the free trial to check 100 emails.