Do as many jobs as you can.
Farming - Only farm blueberries and tomatoes when you have time. When you're going to sleep or to school - farm raspberries.
Bugs - Possibly the best way, but it can be time consuming.
The best tip I can give you is to save up all your crops, panned minerals and mined minerals and only sell it after every two weeks. This would ensure you'll have a huge gralat reward at the end of each week, or two weeks.