One of the basic choices you have is to either have the cables cross underneath or not. Do a search for "california cross". When setting up that way the cables will cross beneath (shifter) and it will make for a "cleaner" front area. Some folks will swear it's required for good shifting and others will say it's not. More important than that is the cable housing length and ensuring each cable housing is not too short or too long. The cables don't know/care which are in front or in back when coming off the shifters.