Here's how you can make sure it's up to standard.
Clear gutters and drains.
Make sure that there are no leaves or other debris that is stuck in your gutter and drains. If there is - remove it. Blockages will mean that the rainwater isn't able to disappear safely somewhere, meaning it will find an alternative way which can cause overflowing that may enter into your home.
If you're not able to do this yourself, maybe because the area is out of reach, then call in a professional that will have the right tools to remove any blockage properly.
Keep an eye open by regularly checking to make sure everything is clear.
When the rain is pouring, it can be coming at you in all different directions, so you need to make sure that everything is closed properly, like your windows and doors. Even the tiniest of gaps can allow water to get in, so once the rain has stopped, go and check all the windows and doors in your home to see if they remained completely dry, or if there's some water around the seal. If it is wet, you'll need to address the issue before it happens again. If you need a quick fix, something like rubber sealant is perfect until you find a permanent solution.
Check the roof.
Another big culprit for water damage is from the rainwater getting in through the roof. You can avoid this from happening by getting your roof checked once a year to make sure everything is okay, or if there are any slabs missing or cracks in the foundation. If there is a problem, you will want to get this repaired as soon as possible, because the moment water falls down on it, that pressure will make everything worse, and it'll end up costing you even more than you were willing to pay.
When the damage is done.
If you were unlucky and the water has already come into your basement or got through any crack in your roof, then you'll need to get rid of it and fast. If left for too long, that's when the mold appears and spreads like wildfire until your floors and walls are covered in it - you do not want this to happen.
The best thing to do would be to call in for emergency restoration help. These are trained professionals that will mitigate the loss and get the structure dry before black mold grows.
If water has entered into your house, or you think it will, try moving as many of your valuables from the bottom floor and take them upstairs. Ideally, you don't want anything to touch the bottom floor as that is where the water will gather. - Stack things on top of one another and make sure you have a phone with you upstairs just in case you do need to call for emergency help, (worst case scenario of course). Then all you can do is wait it out and hope that not too much damage will be done.