Question

Spring is the best season of the year. One reason is that the temperature is not too hot or too cold. Spring is the best time of year to start a new routine.
, it is much easier to get up and go for a run in the morning if the weather is nice.

Answer 1

Here are a few corrected and polished versions you can use, plus a brief note on the change.

Simple correction:
Spring is the best season of the year. One reason is that the temperature is neither too hot nor too cold. For example, it is much easier to get up and go for a run in the morning if the weather is nice.

Smoother/connected version:
Spring is the best season of the year because the temperature is neither too hot nor too cold, so it's an ideal time to start a new routine. For example, it's much easier to get up and go for a run in the morning when the weather is pleasant.

More expressive version:
Spring is my favorite season. With temperatures that are neither too hot nor too cold, it’s the perfect time to start a new routine. On cool, sunny mornings it’s much easier to roll out of bed and go for a run.

Note: I replaced "not too hot or too cold" with "neither too hot nor too cold" for grammatical clarity and added a transition (For example/so) to connect the ideas.