If you're currently in a relationship be careful when using jealousy as a tactic.. as you have something to lose.
The reaction of jealousy has a wide range. He/she may be filled with the sense of urgency that you're slipping away, thus wanting more time with you. The opposite end of the spectrum is the anti-tactic: using jealousy against jealousy. And if he/she starts to find whoever they focus on to make you jealous appealing in some way, they may just leave you for them.
If this is an Ex we're talking about, then have at it. You can use it as a tool to win them back. Or if you're viscous, as a means just to make them feel bad. Either way if it blows up in your face, you're still exactly where you were.
The best method Ive found while you're IN a relationship is to give your signifigant other alot of extra attention for a while, and then switch over to cold. Say nothing is wrong when they ask, but still seem distant. Listen to what they say but keep comments short, like you had to say something. When you're talking to someone else of the opposite sex in their presence, make alot of comments and appear much more focused. Laugh at their jokes a little harder. Make sure to bring up other people in conversations (of either sex, really). Recap stories/jokes/moments like they were the greatest things ever. Again, be careful. If she/he cares about you then they'll start paying alot more attention and warm up alot more. If the interest is already lost, it may not affect them at all or even worse... they're already planning to move on.
If we're talking about an Ex here? It's simple. You are the happiest you've ever been. Don't act bitter. Don't battle. Make it a point to keep contact. Invite them to friend's parties. If they refuse, make sure to mention how great it was. If they come along, pay about as much attention to them as you would 'just another friend'. Even better? Pay ALOT more attention to someone else (opposite sex is even better). DON'T start making out in front of them, or even flirt too harshly (unless you're "going for the throat"). Just skim the waters, and if they dont seem to be paying attention? Trust me they're noticing. Just playing along. That's just ONE example, but you get the idea.
~Look better than ever. Get a tan. Try a different hairstyle. Dress just a little sexier.
~Smell really good. But dont use their 'favorite' cologne/perfume if they have one. Change it up. If you had a specific kind you kept buying because they loved it, make them wonder who you bought the 'new' stuff for.
~Have alot more fun then you used to, and BE alot more fun then you used to. Even if you're not feeling it, faking it isn't hard.
Well I think Ive written enough. Have fun, be careful and the best of luck.