We have been developing a dapp which submits a very basic transaction (placing a short hash and some Eth into a contract). We set the gas relatively high (250000). Often the transaction is mined in good time, within a minute, which is just about tolerable to a waiting user. Sometimes, however, it is very long, occasionally threatening to take hours according to Etherscan.
We have considered e.g. Gas price strategy, but we can't quite see how that would deal with these strange delays.
What can we do to overcome this?
Is there a good description for how to do this?