Part of naming variables wisely is knowing which characters are valid characters to be used in the varname. Valid characters for varnames are the letters of the alphabet (both upper- and lowercase), numbers, and the underscore character. One caveat is that the varname cannot start with a number. For example, consider the following varnames:
Peaches 2Peaches PeachesAndCream Peaches4 _2Peaches
The second is not a legal varname, but the rest are. Notice that the last example begins with an underscore, which is valid. The second one is not valid because it begins with a number.