The only way to guarantee a hatchable egg is to buy one through the store (cash shop or one of the 100DigiCore eggs in the DigiCore shop) or through some sort of promotion/event. Dropped in-game eggs are all about luck, and have ridiculously high failure rates. Some people go through 30-60 eggs without hatching one. I got lucky and managed to hatch an Elecmon, after wasting about 60 Beast data without breaking it, and even then if I had pushed past 3 even just to 4 I know I would've lost the egg.
If you're not interested in paying for your eggs, you'd best start grinding for an assload of eggs and data. If you get an egg to 3 successful inputs, just hatch it to save yourself some time and rage.
Lately it has gotten better. You pretty much need to farm the crap out of a certain Digimon you want(this becomes easier at higher levels where you spend a few days on one enemy). Make sure their name is white or very light red or your drop rate gets nerfed. Leaders seem to have a slightly higher drop rate for them as well. By the time an egg drops you should have a fair bit of data to spin the wheel. Today I spent a fair amount of time killing saberleomons and got 5 eggs and like 50 data
Having a girlfriend is like like paying taxes, you constantly get screwed out of your money, but rarely get any returns. -PeacemakerSAA