It is good to try something new every once in awhile to keep your writing fresh and creative. If you write one genre, then try another that is totally opposite. If you write novel length work, then try a short story. If you are not happy with the result, then don't do it again. Put the experience in the back of your head for future reference, but you might surprise yourself.
Manuscripts can vary from a few hundred words to several thousand.
The shortest length is called flash fiction and it is under 1,000 words. However, it can as short as a few hundred. The longest manuscript length is the novel and can be anywhere from 30,000 to over 100,000 words. In between the two ends of the spectrum are the short story at 1,000 to 7,500 words, the novelette at 7,500 words to 17,500 words and the novella at 17,500- 30,000. These are general guidelines.