Could it be: air bells?

Small, perfectly round clear spots that show as dark dots on a scan or print. Fix: Tap the tank firmly on the bench after pouring in the developer and after each agitation.

Could it be: dust while drying?

Irregular specks and fibres stuck to the surface. Can sometimes be removed with a blower. Fix: Dry film in a still, dust-free room such as a bathroom after running the shower.

Could it be: pinholes from undissolved developer or stop bath that's too strong?

Tiny clear pinpricks across the whole roll. Fix: Make sure powder developers are fully dissolved, and use stop bath at the correct dilution, or plain water.

What went wrong?

There are spots on my negatives

Small round clear spots (dark on scans), or white specks and fluff (dark or white depending on side).

Check this first

Are the spots perfectly round and clear, or irregular specks sitting on the surface?

Likely causes

1.
Air bells
Common
How to tell
Small, perfectly round clear spots that show as dark dots on a scan or print.
Fix
Tap the tank firmly on the bench after pouring in the developer and after each agitation.
2.
Dust while drying
Common
How to tell
Irregular specks and fibres stuck to the surface. Can sometimes be removed with a blower.
Fix
Dry film in a still, dust-free room such as a bathroom after running the shower.
3.
Pinholes from undissolved developer or stop bath that's too strong
Rare
How to tell
Tiny clear pinpricks across the whole roll.
Fix
Make sure powder developers are fully dissolved, and use stop bath at the correct dilution, or plain water.

Avoiding it next time

Tap the tank after every agitation.
Use a wetting agent in the final rinse.

There are spots on my negatives

Likely causes

Air bells

Dust while drying

Pinholes from undissolved developer or stop bath that's too strong

Avoiding it next time

Go deeper

Other negatives problems