I use underscores for spaces in Custom field nameinng. Mostly because thats how salesforce normaly is from the system I came from. So it would look something like this: first_name, last_name, lead_email. On the front end it will look like this: First Name, Last Name, Email. Not sure if this answers your question or not
It's just something ive always done. It limits user error for accidently puting more than once space or soemthing.
Just how I do it 🙂