Voting 3rd party or staying home does nothing to make the GOP more conservative, because the attitude of the RINOs who are in charge of the nominating process is: "Well if the Democrats won it's because our guy was too conservative. We need to find someone more moderate."
The RINOs never react by nominating someone more conservative next time.
Good advice. While you're at it, mention that you should give money to individual candidates - the RNC can and will support RINOs in the primaries vs true conservatives (Toomey in PA, Laffey in RI).