The practice of “casting lots” is mentioned 70 times in the Old Testament and 7 times in the New Testament. It isn’t known what this entailed, whether it was a form of dice or coins or using sticks of various lengths.

The passage you mentioned in Acts 1 is interesting, because it says that the apostles followed this procedure:

1) they proposed two men to replace Judas
2) they prayed and asked for God to reveal His will
3) they cast lots

From this, one thing we know for sure is that it’s important to pray and ask God for wisdom when we seek to know His will.
As for following this procedure every time we want to know God’s will, that would probably be a stretch. It’s the only time it occurs in the New Testament in just this way, so to take this as a pattern would not necessarily be a good thing. Nowhere in the New Testament are we as Christians instructed to cast lots as a way to determine God’s will.

So why did the apostles cast lots to pick the replacement apostle? Hard to say, but just because they did it doesn’t mean it was God’s preferred method. Keep in mind that God often allows us to do certain things, but that doesn’t mean he always approves. What we do know is that we are to pray. This pattern is repeated numerous times in Scripture.

So, in conclusion, we would say that casting lots, or flipping a coin, is not the preferred method of determining God’s will in important matters. On some things, like which restaurant should you eat at tonight, then flipping a coin is probably just fine. But to use that as a determination for who you should marry, or what career you should choose, we would not recommend it, and we don’t think the Bible does either.