Several horizontal and vertical lines, also known as glyph metrics, will help you with your font design. You can activate them through the Metrics Options window.
In order to change the metrics click Properties on the Font menu and then click the Metrics tab.
In the Glyph Edit window there are two vertical lines (normally the glyph outline lies in between these lines) that represent the left and right side bearings. These are shown by default but you can hide them through the Show Metrics button on the Drawing toolbar. The left and right side bearings can be changed by dragging them to their desired position. You can also adjust the bearings through the Glyph Properties tool window. White space should be evenly distributed between the left and right side bearings of glyphs except when font is specifically designed with ligatures for joining characters in a cursive script font.
Note: Lining numbers (i.e. the digits 0 - 9) should all have the same advance width.
Tip: In the Glyph Edit window you can step through with the Back and Forward blue arrows in the Drawing toolbar to make adjustments.