Jisho

もし時間があったら、週末に家族といっしょにテニスをしたいです

もし is optional, but signals to the listener that a hypothetical is coming.

This situation is not particularly unlikely, so you can translate this "would" as したい.

If it's an unlikely hypothetical, like winning the lottery, you would use phrasing that suggests the unlikeliness.

宝くじで１億円当たったら、世界一周旅行に行くのになあ

If I won 100 million yen in the lottery, I would travel around the world.

Just to clarify @Leebo, もし implies that the sentence is completely hypothetical, whilst using the potential form without could be indicating that it is a genuine possibility and, if the requirement(s) is/are met, 'that' is what will happen?