Good question. For a more neutral statement I might write down something like, “My ability to play tennis might not be up to par yet but I can learn and improve” as compared to a positive one (“I’ll be a great tennis player in no time at all”, which seems unrealistic to me) and a negative one (“I’m terrible at playing tennis and I’ll never be any good.”)

I know of a few people who prefer neutral statements as they encourage a growth mindset rather than a fixed one in my experience :)