Wikis are collaborative creations that can be edited and added to by anyone - so you may not always be able to rely on the quality of the information given. Therefore, consider finding a more authoritative source to reference instead. If you do decide to reference a wiki, you will need to reference it as an anonymous entry (unless you can find an author specifically identified as responsible for the content) and date of update.
Anon. (2018) suggests that…
...is why its successful (Anon 2018).
ANON., Year of last update. Title of entry. In: Wiki name [viewed date]. Available from: URL
ANON., 2018. How to improve your study skills. In: Wikihow [viewed 13 July 2018]. Available from: https://www.wikihow.com/Improve-Your-Study-Skills