There are a couple of options:
You can use either SnapLines or SnapToGrid by changing settings here:
Tools -> Options -> Windows Forms Designer -> General -> Layout Mode (and ShowGrid, SnapToGrid)
Note, you'll need to close and reopen the designer for the changes to take effect.
Or, you can align controls by selecting the ones you wish to align and using alignment functions on the Layout toolbar. To display the Layout toolbar, right-click on an empty area of your toolbar (you should then see a long list of available toolbars), and check the checkbox for "Layout".