My Ice-Mine combo never works! I have the breeding cave and I have tried over 35 times! Any tips?
You don't mention in your question, but I assume you're referring to breeding the Diamond Dragon of which the only possible breeding combo is Ice+Mine.
Sadly, the gemstone dragons are extremely rare - the chances of breeding one are typically in the single digits. Additionally, the Ice+Mine combo has some bad failure modes where it will breed long incubation time eggs. Thus, this is arguably amongst the most difficult of the gemstone dragons.
The only things that are known to affect your breeding chances are:
Both of these increase the chances of breeding the rarer dragons, although the overall effect isn't known, and it is assumed to be relatively small.
You may think that the number of times you've tried makes a difference, but this is what's known as the Gambler's Fallacy. No matter how many times you attempt and fail, the odds of breeding are always the same.
As a second thought experiment along these lines, consider flipping a coin. Assuming a fair coin, if you flip a coin 50 times and it comes up heads each and every time, what are the odds of flipping the coin one more time and it landing on heads? Despite what your intuition might tell you ("It's been a while since tails, so probably tails is more likely" or "heads sure has come up a lot, heads is more likely"), the answer is 50/50, the same as it was on each and every previous flip.