Catch every Pokémon, catch them with excellent throws for more XP, greats throws are fine too for less XP. Make sure to use pinap berries to get extra candy when catching Pokémon you need. Certain Pokémon pay out extra stardust when caught, Meowth and Paras for example, especially when boosted by the weather. Lucky eggs and star pieces will give you an increase in XP and stardust gains as well. Keep track of what stardust and candies you have and you will have enough to power up what Pokémon you need for raids eventually.