The exact style depends on the convention of the language I'm using (i.e. camelCase for JavaScript, snake_case for Ruby and Python, etc). As far as the intention you can't go wrong with the principals outlined in Clean Code:

• Use Intention-Revealing Names
• Avoid Disinformation
• Use Pronounceable Names
• Use a Searchable Name

To see a summary (not by me), check out this post. Read the original if you can, as it's got many more sound recommendations that I think more developers would benefit from - it's a timeless classic for programming.

Friend, Two most difficult problems of software engineering is Naming Variables and Invalidating Cache (when to do, when not to do etc).

Use camelCasing (no underscore please) and I am okay with bigger names because at least gives you idea in one go that what it does or is being used for. Try to use similar kinds of word through out the app like if you are using loginButton, follow same pattern rather then saying loginActionButton or something somewhere else.