Leave the large cavern and head back to the large room containing the first Save station. Once you get there, save your game and head right. Go through the next tunnel that was once filled with lava before the earthquake, you'll eventually reach another large cavern where the lava resided. Head down the path and watch out for the spiked creatures crawling along the terrain, they cause a lot of damage. In the next tunnel, drop down the shaft and go right.
You'll find another huge cavern, this time the lower part of the screen will be filled with lava. Cross the platforms above the lava, eventually you'll see a large opening below but you won't be able to go down due to the lava, so head right - and don't fall in. In the next corridor, you'll notice lava filling the holes in the ground, as well as a change in the music playing. Traverse through the tunnel, then head up the long shaft leading skyward. You'll now be in a large shaft leading to paths both up and down, for now head up to the upper one.
Watch out for the creatures coming up out of the ground in the next corridor, if you're patient you can keep firing at them, they'll eventually stop after a while, but if you couldn't be bothered (like me) just head right to find the first ruins area.
Be happy whenever you find ancient ruins within SR388 as they'll without a doubt be hiding tons of items within, most of them unique ones. Go right to find the entrance, then save the game once inside. Head right, then drop down to the very bottom of the shaft there, bypassing an exit leading right. Head through the door on the left, cross the empty corridor and blast open the door at the end with missiles.
Go into the next room to find the Bomb power-up, as well as a Missile Pod. Once you've found them, head back to the shaft and go through the door you bypassed up the shaft. In the next room you'll find a dead-end with a gun turret on the wall. Blast the turret's mouth, then jump on top of the remains and activate the Morphing Ball. Roll right to find a hidden passage, then blow your way through the blocked tunnel to find your first Energy Tank. Go through the exit on the right to find yet another shaft leading up and down - yep, this place is an absolute maze.
At the very bottom of this shaft you'll find an empty corridor leading to a room containing the Ice Beam, so don't forget to pick it up. At the very top of the shaft you'll spot an exit on the left that'll be too high to reach, so don't worry about it now. Two doors will lead off from the right wall, the upper one leads out of the ruins, while the lower one leads to a room with three Missile Pods to be found.
If you're having trouble reaching the one in the roof, come back once you've found the High Jump Boots. A secret passage on the right side of this room leads to the room containing the Spider Ball, but you won't be able to reach it, so instead head back up the shaft and go through the upper right door to emerge back out of the ruins.
Back outside, head to the right of the cavern to find a Metroid's empty shell on a ledge - whenever you see one it'll mean that a Metroid's nearby. Go through the exit on the right and head through the next corridor, using the Morphing Ball and bombs to get through the small passage. At the end of the corridor you'll spot a shaded tunnel leading down between the bricks, so take the plunge and drop down.
Drop down to the bottom of the next room through one of the two narrow passages to find the Spider Ball. You can now try out this nifty item unique to this game (except now for Metroid Prime ;)). Use the Spider Ball (press down while in Morphing Ball mode to activate) to get back up to the corridor above, then head left back out to the ruins. Once you spot the Metroid shell again, climb up to that ledge and use the Spider Ball to climb up the wall on the right. Go through the opening you'll find above to face the second Alpha Metroid.
Once you've blasted it to Metroid-heaven, go back over to the ruins, and use the Spider Ball to climb up to the top of the ruins (you can either climb around the cavern walls above or go back into the ruins and climb back out over the roof). Traverse over the roof until you reach a cliff, then drop down to find an opening leading into the ruins blocked by a small boulder. Use a bomb to destroy it then head inside. While crossing through the next corridor you'll find two Missile Pods.
Once you've found them you'll have cleared out the first ruins area, so it's time to leave. Go back to the western entrance and head left (don't forget to save first). Watch out for the creatures flying up out of the nests in the next corridor, once you reach the shaft leading down drop down to the base of the shaft and head right.