You can set the following preferences in the Snapping category of the Preferences window.
To return to the default factory settings, choose in this window. Note that this resets the preferences in every category in the Preferences window.
With these options, you can control the size region around the mouse pointer that is used for the snap operation.
When on, the snap region is restricted to a square area around the cursor, defined by the Snap tolerance option. When off, the snap region is unlimited; you can snap to anything viewable.
Controls the size of the snapping area around the cursor when Use snap tolerance is on. For example, if you have two curves close together and you try snapping to one of the curves, the object may snap to the wrong curve. To avoid this, try using a small Snap tolerance value.
This preference defines how close UVs are together before they snap when moving and using the v hotkey (snap to points).
Controls the number of magnet points inside edges. For example, 3 means there are magnet points at each end and in the middle.
Controls how “sticky” each magnet is; that is, how close the point must be to a magnet before the point snaps to it. Set this to 100 to constrain points to always be at magnet points.