Continuation Bets

About how often do people like to make continuation bets after missing the flop? I find if I do them every time, people catch on real quick. I've been working on a strategy for Hold 'Em NL that tries to randomise these bets. A similar approach may be applicable to other games:

Amount:

2/3 - against 2 players, or with 2 suited or 2 consecutive cards on the flop
1/2 - against 1 player, no suited or consecutive cards on the flop

Early/Mid Position:

Against one player: Unless an A or two of JQKT flops or I hold two red cards.
Against two players: Unless an A, T, or two of JQK flops or I hold exactly one red card.

Last position:

Against one player: Unless I hold two red cards
Against two players: Unless an A or two of JQKT flops or I hold two red cards.

The red cards are to randomise so I don't become predictable.

Any suggestions on this strategy? Of course, I'd mix it up if someone were particularly weak/prone to calling.