The nutrition offered to your budgie through their diet, is extremely important if you wish to watch their development and growth. A proper diet should not consist solely on one source (such as seeds) but have a varying mixture of seeds, pellets and fresh foods, however, some foods can be toxic to your budgie, so be careful.
Dried fruits or veggies in a seed mix are no substitute for the fresh foods you should feed your budgie on a day to day basis. Some seed mixes add colors and even flavors to the seeds. Avoid any mixes that use artificial colors or flavors. Keep the seed fresh by keeping it sealed in an air-tight container.
Many people don't realize that seed isn't the only thing a budgie should consume as a part of their diet. In fact, budgies on a seed-only diet are known to suffer from malnutrition and related complications, such as obesity, and will live far shorter and, not so healthy life. Budgies quite often enjoy fresh foods slightly wet, so be sure to rinse first and put greens into the cage while they are still dripping wet. Some fresh foods that budgies typically enjoy include carrot tops, sprouts, strawberries, apples, broccoli, and most dark, leafy greens. When you feed lettuces to your budgie(s) avoid those that are mostly water, such as iceberg and cabbage, as they are low in nutrition and the high water content which can cause loose stools. After a bit of time you will come to grips with your budgies like and dislikes and will be able to tailor their diet to their needs. Be aware when feeding a budgie that too much of a good thing can be bad, a good rule of thumb when feeding fresh foods to a budgie that you supply a little more than a fingernails worth.
Some hazards, and foods that should be avoided at all costs because they are deadly for birds. Never feed your budgie: chocolate, mushrooms, avocado, fruit seeds and pits, uncooked beans, tomato leaves and stems, and rhubarb. Many fruit seeds and pits are toxic to birds, so you should always remove fruit seeds or cut away parts of fruit that touched the pit.
Always make sure you change your budgie (s) food daily, and supply fresh fruits and vegetables constantly. I buy seed from a breeder and my budgie loves when I sprout the seed and give him freshly picked sprouts. Never be afraid to try new things either, just do a quick Google search to find out if there OK.