1)Once you make the preserve, you can keep it for 2 weeks in fridge or more if you freeze them individually in ice cube trays.
2)Try to use little sour mangoes for this which has the tart taste which balances nice with the sugar and the spices..If your mangoes are not that tart, you can add extra lemon juice in this.
3)You can even add some crushed mint leaves in this for more flavour.
4)Cooking mangoes with skin is important, this make the flavour of raw mango stands out.
5)You can add jaggery instead of sugar in this