You start mining at Neitiznot South via the skills teleport.
Buy a pickaxe from Bob (Iron for the first rock, from then on rune) , then teleport to Neitiznot North or Falador cave to start mining.
Falador cave is advised as soon as you're 70 mining, as there are 2 adamant rocks next to eachother.
mining is also the gathering profession related to smithing, smithing is one of the best money making skills @ low lvls