After reading a lot of different sources, here is what I do. I'm sure there are many variations.
Mine are fed in shallow dishes on the floor of the cage, because they are ground feeders, and that is where they love to eat.
*I offer Roudybush crumbles in a small bowl. They don't eat much of this, but it is sort of a back up.
*I offer a mix of seeds which is their staple: 1)Goldenfeast Australian Blend, 2)a good finch blend (right now 'Smart and Sassy'), and 3)a 'small hookbill' or cockatiel blend (also 'Smart and Sassy'). There are other good brands and mixes. I like these products because they also have herbs, dried greens, etc., mixed in with the seeds.
Proportions are an even 1/3 of each. I mix up enough for a week or two and keep it in the fridge. The rest goes in the freezer.
*Lastly, I make up 'chop' (there are many recipes) and freeze in ice cube trays. Once frozen, they go in containers in the freezer. My two get one cube (defrosted the night before), mixed with a little sprouting seed to tempt them to eat it. Chop is good for about 3 months in the freezer.
Sometimes I sprout seeds and give this during the day instead of their regular seeds. I always remove this in the early evening and replace with some regular seed mix.
They also have cuttlebone, a mineral block and a calcium block. They love the cuttlebone.
I also try to put in something fresh every day in their cage like kale, broccoli, chicory, etc, in a little water to keep it fresher.