When it comes to subscribe forms and dedicate subscription landing pages, it's pretty common sense that you should apply all of the conversion optimization strategies that you can.

The top three things you should definitely focus on are

1. A CLEAR CTA (GENERALLY A BIG BUTTON).

Here is a great example from Unbounce:

2. SOCIAL PROOF

Buffer nails social proof on all of their subscribe forms:

3. COLLECT RELEVANT DATA BUT DON'T GO OVER THE TOP

Collect data that is useful for segmentation but don't ask for too many fields. A long form usually reduces conversions. This example from HubSpot shows how it's done: