keep it short, well heard and to the point.
As a LEO myself, I think one aspect of a citizen's arrest-type situation is being overlooked: The longer you have the bad guy around, the more likely he is to try to jump you. Doing a solo arrest, with no cuffs and no experience is pretty dicey. A better approach might be "get out of my house or I'll shoot you" or if approached elsewhere "get away from me or I'll shoot you." Confronted with the opportunity to leave or get shot, most bad guys will take the opportunity to leave. They can always go rob someone else.
Survival should be the first objective of the armed citizen. Whether the bad guy gets caught is secondary. Be a good witness, file a police report.