You will need to be able to get into the mining guild, if you are not able to get into the mining guild; you will need to raise your mining level, to level 60.
Follow my other guide on how to get to level 60 mining for help
You need to mine 200 coal from the mining guild, there are usually a lot of people in guild but there are plenty of rocks to go around. This should only take you 8 trips to get around 200 coal in only about 1 hour.
Now you will need to get 100 Iron which is much faster to mine, and since you only need 100 it shouldn’t take too long, I wouldn’t be surprised you were able to get 100 iron in just under 10 minutes.
Take the coal and iron and start smithing to make 100 steel bars
Note the 100 steel bars and deposit in the grand exchange, and you should make around 50k
Repeat steps 2 – 5 until you are satisfied =)
So you should be able to make 50k a day if you use this method, you can however make more than 100, but you will eventually get bored and give up, by keeping it at 100 steel bars it does not take too long and you can see the results right away to keep you motivated. And guess what! If you keep making 50k a day, for 20 days you will have made 1 million