I think using A310-300 is a kind of art.
First, to secure the pax supply, you need to base in some major international airport, that can provide a lot of routes that can allows you to fly for a long range. (If no long range routes, why don't I just order B757?)
Second, you shouldn't use it when you face vigorous competition, once the LF% drops, you must the one who generate loss instead of your competitors. (Normally minor long haul routes (150-200 Pax) do not have competition, but if your competitors are in the same base with you, you will probably got attacked by them, even they use L1011 can generate profit on the same route but not you.)
Third, to ensure you have relatively low maintenance cost, you must use it with the super-profit generating aircraft A306/A306R, they can reduce the maintenance cost of A310s and earn money to save you when you are in high fuel price.
For my experience, I am using to fly five routes a week, LHBP, EGKK, VRMM, SBSV and OLBA, which really contains all kind of destinations. The profit is not really good when just threw them in, but if the RI goes high, the situation maybe better.