Feeding according to packages isn't a good idea because, well, pretty much any betta will try to eat the whole package if you let them.
Yeah, a good way to figure out how much to feed is that their stomach is about the size of their eye.
So most people (myself included) feed them twice a day, with a total of 4-6 pellets. However, if you find your betta bloats, you feed him less.
Here is my schedule:
Monday- 2 pellets in the morning, 2/3 at night
Tuesday- 2 pellets in the morning (different brand), 1 pellet and a piece of FD brine shrimp
Wednesday- Same as Monday
Thursday- One FD bloodworm in the morning, and one at night
Friday- 2 pellets in the morning (one of each brand), 2/3 at night
Don't forget to presoak all of your betta's food in some tank water before you feed it to them! Pellets and FD foods will expand inside your betta otherwise and can cause bloat or constipation.