Summarize this article:

Once you've placed your bridge, you'll want to check to make sure its placement is correct. Lay your violin down on a flat surface. Get down to the violin's level. The side of the bridge facing the violin's tailpiece should stand at a roughly 90 degree. The other side of the bridge should be sloped forward slightly. If the bridge is not forming a 90 degree angle, you may have put it in place backwards. You'll have to remove the bridge and start over. Your bridge should be in the center of the violin. It should not be too far to the left or right. If your bridge is leaning to the right or the left, gently push it until it's in the center of the violin. You can simply eyeball to see if the bridge is in the center by glancing at the violin from a bird's eye angle. If you want to be extra sure the bridge is positioned correctly, however, you can use a ruler or measuring tape to measure the length of each end of the bridge to the end of the violin. The measurements should be roughly equal. The bridge should be between the f-holes, roughly falling between the middle of each hole. The bridge may have slipped slightly while you were tightening the strings, so once again check. Make sure you can drawn an imaginary line through the center of each f-hole that runs through the bridge. If the bridge has moved, gently slide it up or down until it's in the right place.

Summary:
Make sure the bridge is standing at a 90 degree angle. Check to make sure the bridge is in the center of the violin. Make sure the bridge falls roughly in the middle of the f-holes.