Ditto

Theres really no tips or tricks, sadly. Just catch any ditto eligible species that you find, try to see if theres a local group chat that can help you and hope for the best.

The only suggestion I can give you is to try to find an area where Pidgey, Rattata and other "Ditto-Pokemon" spawn a lot and then just catch everything you see. Atleast that should give you a better chance at finding one.

I did that when I reached "catch a Ditto" in the Mew quest and found one the same day. And then another one. Then two more the next day and when a local player reached that part a couple of days later I joined him there and found another one.
I think I got like 7-8 Ditto in a week.

Catch everything that can turn into ditto.

I find that certain locations spawn them more. Especially at Starbucks but I may be imagining it

Check with your local resources if you have them. Find a place that spawns a lot of mons. There’s a place I went to with 4 stops that also produced dittos often. I got a Starbucks, lured up the stops and within an hour I got mine.

I wonder if trading a Ditto would work... My guess is on no, but it's easy to try and there is no risk of losing anything so you might try that.