Depends on the quality and age of your tent,
For an older tent you first want to buy some seam sealer and seal every sewn seam on your tent.
Then get some silicone waterproof and paint the whole tent.
Let it air out and dry really well, (fumes hang around )
Cut a plastic foot print for your tent to go underneath when you set up. You should be able to roll it up with your tent.
or still using your foot print, carry an extra tarp to be able to tarp yourself in, it must be large enough to cover an area bigger than the tent so the water can not be blown in.
Even with a new tent I would make a foot print because it will prolong the life of your tent floor.
I hang a tarp over my tent if needed in case of rain and angle it so water drains off, Have not had an issue as yet, not even with the wind
I always pack a couple of 8×8 tarps , hang them from trees over your tent or just throw it over the tent in a pinch . They are also handy to create shade , and use for ground sheets.
In the case of heavy rains and pad slopes, dig a small trench around the outside of your tent to help prevent puddling at the base (a plastic or tarp footprint is also a must!) Make sure to fill in your little trenches when you leave!
When I buy a new tent I make sure to give it a coat of waterproof spray.Also if my tent doesnt come with a foot print, I make one out of a tarp.If I know it will rain I even place an extra tarp over the tent. When I place the tarp I make sure it doesnt touch the tent it self.I usually use trees around to tie it up.