What version of filemaker are you using?
In filemaker 11, you'll find a number of tools to help you with this on the Inspector tab. You can, for example, select a group of objects such as the fields in a portal and choose an alignment option to align them all by top, left, right, middle, etc. You can also specify text alignment in the paragraph section on the appearance tab of the inspector.
On the position tab, you can click an object to see its position and dimensions. You can change its position by entering a new value in one of these boxes. You'll find that easiest to do if you click on the units until they show "pixels" so you can make changes in terms of the number of pixels.
You can also resize an object by clicking it and then dragging one of the selection boxes that appear on the object's corners. You can hold down the shift key to lock the size change into just one direction and you can also resize the portal itself in the same way. You can actually redesign your portal from the default appearance until it resembles a miniature "form view" of your portal data instead of a "table" like view if you want.
Finally, you can "nudge" objects while in layout mode by selecting them and then pressing an arrow key to move the object one pixel in the arrow key's direction.
All of the above techniques are available in older filemaker versions. They're either located in the Format menu or on the Object Info palette.