Dos and don’ts

Do’s

Always backup your key on an encrypted device stored safely;
Generate subkeys for daily activity, as they can be revoked easily;
Try to store your primary key offline on an encrypted device;
Consider generating a revocation certificate that you’ll print and store safely, it might prove useful if you lose control on your primary key;
If you create a shared key (eg a GNU/Linux distribution release signature key or for release signature key of a FOSS project), have a clear and shared key management policy. Ideally the primary key should be offline and the less accessible that it’s humanely possible to do without creating unwarranted privileges for some persons in the sharing group;

Don’t share your personal private material with anyone;
Seriously, don’t do that, and don’t think that the GPG system in ProtonMail is safe (most FOSS environments won’t give trust to a personal key that one doesn’t exclusively own and manage);
If you manage a shared private key (distribution release signature key or something else), don’t ever divert from the key management policy set up collectively;