"Hi. I'm fairly new to constructing and I have some questions about themes.
1) Can you do a straight theme (names of the members of the Rolling Stones band just as an example?) Or does the theme need some wordplay ('Charlie Mega Watts' for instance, with a 'Power Stones' theme?) (I'm not serious about this particular idea, so if you want you can try and make it work!) It seems like lately all themes involve wordplay.
2) Can I get away with some non-theme words that are larger than my theme words? For example, say 2 11s are themed, but the puzzle also has a 13; can it not relate to the theme?"
There are specific rules on word lengths: No non-theme entry can be longer than a theme entry. There are two exceptions to this rule:
1) If all the theme entries are horizontal, an editor may allow a vertical entry that is longer than the shorter theme entries, but they probably wouldn't like it if the vertical entry was longer than all the theme entries.
2) All of the theme entries but one can follow a rule if the last theme entry defines the rule (typically the clue for that entry is something like "Theme of this puzzle", "Another name for this puzzle", or maybe "Movie which co-starred actors hidden within 17A, 23A, and 57A"). Occasionally, there is more than one theme entry which defines the other theme entries..
Straight themes are fine. If you look at the NYT puzzle as an example, Monday is almost always a straight theme. Beginning solvers have a much easier time with straight themes. But even a straight theme needs to be consistent. You couldn't have a puzzle with JOHN LENNON (10), RINGO STARR (10), and PAUL MCCARTNEY (13) and leave out George (leaving out Pete Best is fine). With a group such as the Stones or the Dead, which has changed members over the years, the important thing is that the solver feels it's consistent. If the set is small and fixed (e.g., FDR's Vice Presidents), you need to have them all. If the set is large (e.g., US Vice Presidents), obviously that's not the case.
Wordplay themes also need to be consistent. Suppose you had JOHN LENIN. You couldn't match that with KEN STARR, for a number of reasons:
1) KEN STARR is real; JOHN LENIN isn't.
The reason for the need for consistency is that you want to avoid a situation where a solver can make an incorrect assumption based on a subset of your theme entries ("I get it, it's homonyms of Beatles names...").
As for what editors like in a theme, I can only say that they vary (and it seems to me more so with regard to wordplay), so solve (or at least review) puzzles of the editors you're targetting. For example, if I didn't get around to solving a daily NYT puzzle (or my wife solved it before I got to it :), I always try to look at the answer grid before discarding it. This helps me learn what Will Shortz likes.
Hope this helps!