You can also select objects and use the arrow keys to "nudge" them one pixel at a time and you should take a look at the position tab in the inspector, You'll find controls for aligning and distributing a group of options there. These include the same option davidanders has described plus a few more options for aligning objects on your screen.
Nope. these are just the manual tools, which I use all the time. Here's the issue. Suppose you have two columns of fields on different parts of a layout that you want to adjust the spacing vertically. Set the grid to the desired spacing and then drag the fields to the grid. It doesn't work. The old fields will not align to the new grid by dragging. You have to manually align them with the tools. The hard part is getting the fields in the two columns to have the same vertical spacing. There should be some way that you can use dragging to get the fields where you want them without resorting to the tools.
Drag the column so that the top field correctly snaps to the new grid. You may need to adjust the position of the top field individually. Then lock this field. Adjust the bottom field the same way and lock it. Then select all the fields in the column and click the distribute vertical space tool.
That's the best I can think of for adjusting the spacing of a column of layout objects to fit a new grid.
Group the objects after distributing the space vertically to get even spacing.
Align the top object to the correct position.
With the group selected, drag the resize handles down or up to change the spacing.
I think you can use the height box on the inspector's position tab to adjust the spacing of a group of objects a few pixels at a time, but haven't tried it.