Did you grow it from seed? Which variety is it? There are many different ones. Once established, the trees need the soil to dry out, and hate wet feet (roots). Only water it in hot weather, and no watering in colder months. Is it outgrowing the pot it's in? Does it need a bigger pot? Temperature is important for them, but over-watering is a big killer, which it sounds like is happening from your leaf problem.

Have a look at this site for some ideas...Growing Tips

could we see yours

Is it inside or outside? Probably needs rain water, better drainage and higher humidity. Spraying leaves will not help and may contribute to the problem. Buildup of salts and minerals in the soil will contribute to burnt leaf edges as well. Go easy on the fertilizer.

I would say that increasing room humidity with a humidifier would be your best best. They really hate growing in a desert climate.