Just to add to the existing answer.
Even if your transaction is mined in a block it does not necessarily mean it will stay in the canonical chain. It will probably be in the canonical chain at some point but it's impossible to know when.
If the block is not part of the canonical chain it will basically be reverted - which will not hurt your subsequent transactions as a reverted transaction is still a valid transaction. But if it's imperative for you that the transactions are seen as mined in a certain order you have to wait for X confirmations before sending the next transaction (where X is a number of your choice). A
confirmation here means a block on top of the transaction in question.
In theory all transactions in the current Ethereum blockchain may be reverted some day but the more confirmations there are for a given block, the less likely the event is. This is also why exchanges require X amount of confirmations for a transaction before accepting it.