[EldrickOnIce]

My advice, which is far easier said than done, is to hold on to all your dust. Until maybe level 30.
All my 'prized' Pokémon were easily surpassed (and since sent to professor) by simple evolutions at 30 or beyond - and I wasted a lot of dust on ones I junked, including a bunch initially with low IV.
In my opinion, you need about 12 Pokémon to drop in gyms, with high CP the only thing that matters. You need another 10 big guns with great attacks, for tearing down gyms.
You need a mix in the 1000-1200 point range - grass, electric and water Pokémon with best attacks - for building gym prestige, maybe 20 Pokémon in total in those groupings.
I could throw the rest away - don't ever use them, even though at times I probably could. Have also tossed out anything not 'strong' or 'amazing' (red appraisal - other colors use different terms) and I'm sure I wasted dust on many of them too.
If your Pokémon doesn't fit that criteria, or whatever your own may be instead, save your dust for when you really need it.

As I said - easier said than done lol.