Ideal chainline puts the gap between the two chainrings in line with the middle of the rear cluster. Spacers between the rings are not a good idea; that will allow the chain to jam between the rings when shifting between them. Chainline adjustments can be made by adding a spacer under the flange of the fixed cup to move the crank outward, or by using a shorter bottom bracket spindle to move the crank inward. Some cartridge bottom brackets allow side-to-side adjustment of the whole cartridge, e.g. Phil Wood. Most inexpensive cartridges do not, although spacers can sometime be installed on the drive side to move the crank outward, and a cartridge with a shorter spindle can move the crank inward.