Usually a specific Angry Bird will perform better in certain level. Learn their powers and advantages and choose the bird that is best suited. After you have started a level with a specific bird, you cannot switch until you restart or the current bird runs out of attempts. Some levels may require that you have your birds work together. For example, sacrifice one (such as Bomb) to destroy large obstacles and clear the way for the next bird. Although each turn places random obstacles on the map, they ones you start with are usually worse.
Bonuses
Connect to Facebook to be able to check your performance against your friends. You will also be able to ask them for energy in order to continue playing.
Power-ups
You can win power-ups as you progress. You are not forced to spend any money to get them. Save them to use at the correct moment. Consider playing a level a few times without using power-ups before using them when needed to complete. Never use a power-up at a time when you have a bad spin; save them for when you have a better chance of completion.
Starting bonuses or penalties
If you get a bad spin from the wheel at the start of a level, it may be impossible to complete on that attempt. If this happens, consider using it as a trial run to plan a strategy for next time.