Chibi ghost is writing nonsense, there are no twigs. Note this thread is about Minetest Game.
When you have more than 2×99 coal lumps, craft them into coal blocks to save inventory space. This is very efficient when you have tons of coal. The same trick works for ingots, mese crystals and diamonds. All these blocks can be reverted to their original form.
Before you go mining, ALWAYS bring enough sticks, wooden planks or tree blocks with you. Nothing is worse than breaking your final pickaxe and then getting stuck in the mines because something is blocking your way.
In your inventory, craft tree blocks only to wooden planks or sticks when you need them. This is another trick to save TONS of inventory space.
The wooden pickaxe is the only wooden tool you will ever need, the other tools just suck too much; don't bother crafting them. Upgrade to a stone pickaxe as soon as you can, throw away or burn the wooden pickaxe and craft the other stone tools instead.
If you can't find coal to operate your furnace, remember that you can always use other fuel sources (mostly wood-pased). Jungle Tree is a very good alternative and almost as good as a coal lump. See here for a list:
http://wiki.minetest.net/SmeltingFor efficient mining, there are two “magic” heights you have to reach:
The first one is Y<=-256, from which diamonds appear, and the second one is Y<=-1024, from which mese blocks appear. From this point on, mese blocks will appear and all ores appear at their maximum probability. Therefore, it is best continue mining at this height as soon you reached it, don't waste time in higher levels.
But it is pointless to dig much deeper than that height as you won't find more things as you go deeper.