Build the outside ring with the top of the mountain tile, also put down the ground tile all over, all on layer2.
make it at least 7 tiles on each side, if your using the Pokemon Essentials pokemon starter kit.
put in the tiles for the pathway, like so, this is how i do mine.
this part is more difficult, but after awile you will learn to do it in less then 30seconds like i did.
continue with adding the wall tiles, make them look good add randomess and make it seem like you really tried, you canot rush a cave.
this part will take about 20-30minuts maybe more depending on how long it takes you and how big the map size is.
on 3rd layer.
Now we will be adding some distractions, to disctract the fact that theres open spaces, try to do something like this,
Alright this one didnt go so well for this step. not as much open space as i thought was going to happen.
Now to add layers!
just add more and more of the wall tiles untill you get a depth feel, i say 3layers is good, maybe in some spaces 4.
Note: This takes the longest to do.
Thats pretty much it, just add props and doors and ladders and what ever you need.