If it doesn't present, practice writing every day.
→ If it doesn't present, practice writing every day. is grammatically incorrect because "present" in this context doesn't make sense. It seems you might want to say:
If it doesn't rain, practice writing every day.
(Assuming "present" was meant to be "rain" or some other verb.)

Unless you return this book today, you’ll have to pay a fine.
→ This sentence is correct. "Unless" is used correctly here to express a condition (if you do not return the book today).

Unless you go out more often, you might fail.
→ This sentence is correct as well. "Unless" is used to show the negative condition, implying that without going out more often, failure might occur.