Try to get about 90% of heat fuel material for good briquettes that will give you more fire. Get materials that will emit less ash, for example, very fine charcoal fines may have come from tree leaves and have a lot of dust and soil in them, will give more ashes after burning. Larger fines are very good and you just need crush them to appropriate size. You can choose wood charcoal, charcoal fines, minerl carbon, coal, biomass as heat fuel material.