"Don't be jealous" is the optimal solution. I guess that's not very helpful but it really is the best course of action.

As someone who has dabbled in polyamory:

I think learning how to get rid of jealousy is a process, but a very doable one (people are off-put by how little I care about previous partners, for instance - my roommate and some of the people I date don't seem to understand it). The funny thing is I am now much less jealous/made insecure by other dates/previous partners (I am not actively practicing polyamory and can't confess I'm very interested in doing so at this time) than I was when I was in a polyamorous relationship, or at least when I started being in one (the relationship spanned about 2 years).

I think it helps to date a ton of people and potentially a ton of people at once, and by "date" I do mean the very casual "seeing someone" as opposed to "have any sort of committment" with them. I think if you start with that framework, of "I don't expect them to have any commitment to me nor I to them" and you start to understand the really enjoyable aspects of that framework, and understand that until there is an established agreement to monogamy there is no expectation and indeed no right to expectation or offense if either date-r is non-monogamous, then it sets you up better for a relationship where you can continue to hold onto those values.

Polyamory doesn't really interest me for other reasons, but I'll tell ya what - not being jealous always interests me. I don't consider jealousy an attractive trait, and minimizing it in my own life is definitely something I'm glad about. Other people look at you askance though. My own roommate has tried to make me feel guilty for seeing multiple people at once. She doesn't understand that until you have a discussion about monogamy there can't possibly be any expectation that either party is monogamous.

Then again she's also ragingly insecure, so... (From my limited, anecdotal experience, people who are ragingly insecure seem to believe you should just kind of 'be monogamous' from the start if you start seeing someone you are interested in. I'm like "All your eggs in one basket, does that sound like a familiar idiom to you? one that doesn't usually end well?" )