Tune it for your best power, then back off a bit for better oiling and richer mixture, which tends to prolong engine life.
Running right at max power jetting tends to be harder on parts and takes more attention to plug chops and such.
For normal riding, just keep going till you're happy and if you're not sure how far lean you are, back off a size. Check the plug for a few days to be sure, then ride it!
If more is better, then too much is just enough.
If you can't afford it, build it yourself.