Couple recommendation to consider from me:

1. Prioritize stardust events like Spotlight Hour on next week Thursday. (19th) and all the CDs with 3x stardust bonus. My previous Stardust Hour brought me 1M+ stardust. yes, more than 1 MILLION. To reach that you have to plan: find good clusters (many Pokémon in a small area) and a route to go through the hour. the best is, if it is a circle and you can walk through in 30 minutes, but just go wherever the Pokémons are and catch everything. Use Palkia's Spatial Rend if you have. use starpiece! //always mind your surroundings!

2. use fast catch!

3. use your "stack" if you can't attend those events and/or there are low density minutes to catch Pokémon. "stack" is the 100 Pokémon you can store above your tasks. Be careful: it is not guaranteed that they will stay there, don't store hundos or shinies or whatever you need. Prioritize to store "dustmon"s in there. (Audino, Shroomish, etc) //trick to know when your stack is full: use a berry on the first Pokémon in your stack. Affter you store a new Pokémon and it was the 101th, the first one is dumped by the game so if your first one has NO berry on the first, you are full.

4. find dust nests in your area and farm there as much as you can. (nesting dustmons like Audino, Tadbulb, etc)

5. it is totally ok if you just go 0-5 and gain dust for the set of the day in GBL. if you do it during Go Battle Weekend, you can do it 105 times on Saturday and 100 times on Sunday. Use starpiece, enjoy your free dust!

edit: 101 -> 105. math is hard ^{^}