If you soak the sticker in soap/water, will the sticker still be sticky?
why do you want to do that?
Well what do you mean that you use a soap/water solution
If you have a soap and water solution and your graphic is a sticker made of "vinyl". The solution will allow you to have play with the graphic. Spray the solution liberally on the area of the car where you want to place the graphic. Place the graphic on top of the solution. Squeeze out all the solution using a squeegie or your terry cloth towel. Doing this will get rid of all the bubbles.
If you place the graphic on the car directly without any solution sometimes you will end up messing up more causing giant air bubbles, wrinkles in graphic, or dust getting trapped beneath the graphic etc. etc. etc.. And you won't have any time to move around the graphic.
Some people do the opposite instead of spraying the area they spray the graphic. Example instead of wetting the car they will soak the graphic in the solution. This will take longer for the vinyl graphic to stick and dry up and adhere to the area. Just make sure it is liberally sprayed not to much or to little. If you put to much just work the solution out it'll eventually stick. It will just take longer for it to dry and stick.
*Remember* If it's vinyl just make sure you use solution if you're not a pro with vinyl. It's just safer and you won't run into errors.