The section of the game that takes place Bikanel Island, including visiting the Al Bhed hometown called “Home” and traveling through the Sanubia Desert, occurs after the events at Lake Macalania.
You start off in the Oasis of the Bikanel’s Sanubia Desert once you regain control of Tidus. Notice that Tidus starts off by himself and he is the only member of your current party. You will have to engage in a battle with just him in the party.
Start off by saving your game at the Save Sphere and then jump back into the water to grab a treasure chest on the lower left side of the pool that contains four 
Remedies.
Walk forward into the desert and you will be thrust into battle against a Zu; a giant bird-like creature. Tidus starts off all by himself at the start of this battle and will be joined partway through by Auron. Lulu will join the battle shortly after that.
Using 
Haste on Tidus (and your team members) and using Slow on Zu can make this battle significantly easier.
Continue northward to find Wakka sitting under some scrap metal. The treasure chest beside him contains an “Al Bhed First Aid Kit” which will allow you to obtain 
Al Bhed Potions from treasure chests in the area.
You will run into large enemies in Bikanel Desert called Sand Worms. They aren’t too difficult to defeat, but they do have a ton of HP, which makes defeating them take quite a while. You can instantly kill them though if you have Auron use his Shooting Star Overdrive on them when you encounter them.
As a result, it can be very helpful to store Auron’s Overdrives for later use as you travel through the Bikanel Desert.
There may also be an 
Al Bhed Primer near Wakka if you have missed any of them thus far. There won’t be any though if you have not missed picking up any so far. Continue northward when you’re ready to head to the next area.
The Al Bhed Potions can only be used by Rikku using the 
Use command. They heal for 1,000 HP and remove the Poison, Silence and Petrification status effects. This means that Rikku can act as your interim healer while you are missing Yuna (once she rejoins your party, that is).
Head into the little alcove to the right to find Kimahri aimlessly trying to climb a sand dune. Not the smartest cat around…
Head backwards once you have met up with Kimahri and head around the dogleg and continue following the trail until you run into Rikku.
The treasure chest next to where you find Rikku contains two 
Ethers. Do not forget to save at the Save Sphere which is essentially a free opportunity to heal up your players now that your primary healer (Yuna) is missing.
Follow Rikku in behind the scrap metal. During your first fight with Rikku back on the team you will get a quick explanation of how using the Steal command on an Al Bhed machina will destroy them in one hit.
There will be a noticeable area that extends off to the left as you continue down the pathway. Following it will lead to a treasure chest that contains four 
Hi-Potions. Continue along the trail into the next area.
You may eventually run into a Cactuar in this next area. Cactuars are a tough enemy. They have very high evasion and heavy armor, which means that even if your attacks do manage to hit the Cactuar they will do very little damage. They also unleash some pretty devastating attacks including 10,000 Needles which does 10,000 HP worth of damage making it an instant kill.
That being said, they give great rewards for defeating them, including armor, weapons and a very large amount of AP. The best tactic for defeating Cactuars is to save up your Overdrives during your time in the Sanubia Desert and use them if you run into any Cactuars. Your Overdrive attacks cannot miss.
Follow the red arrow into the center of the next desert section. There is a treasure chest in the center of this area that contains four Hi-Potions.
Just southwest of this treasure chest is a rock formation that is shown on the mini-map. On the opposite side of the rocks is a treasure chest that contains two X-Potions. Finally, at the far west corner of the map there is a treasure chest that two Mega-Potions.
Make your way to the Save Sphere located north of all of these items. The sign next to the Save Sphere reads “Beware of fiend! Weaker fiend to the right. Stronger fiend to the left.”
Go west from the Save Sphere into a small enclosure and you will find a treasure chest that contains an Elixir (to the south) and the enclosure to the north of this area has two treasure chests - one of which contains a 
Lv. 2 Key Sphere and the second which contains 10,000 gil.
Just north of this area you will find an Al Bhed Primer (Vol. XVII) sitting on the ground.
Go back to the Save Sphere and head straight north towards a sign post in the distance. Lying just below that sign post is a book on the ground, specifically Al Bhed Primer (Vol. XVIII). Continue north from here into the next area.
Just in case you are curious, there were two paths leading northward in the last area and they both lead to this same region so don’t worry about leaving any of the areas unexplored.
Continue north through this region until you see a small area off to the left side on the mini-map. There is a treasure chest along the way that yields eight Hi-Potions.
West from there, at the bottom of the sand whirlpool, is a treasure chest which contains the 
Mercury Crest. This item is needed later on to obtain Rikku’s Celestial Weapon, the 
Godhand.
Northeast of this area are whirlpools with treasure chests inside of them. Once you touch the treasure chest you will be thrown into battle against a Sangragora. Sangragora are relatively easy to defeat other than the Confuse status effect that they can inflict on your party members.
Equip your characters with armor that has the 
Confuse Ward or Confuseproof ability to make these battles much easier.
The first treasure chest contains three Megalixirs. The second chest contains two 
Teleport Spheres. Read more about Teleport Spheres in the Sphere Grid section of the strategy guide. These are great items to pick up so it is definitely worth engaging in battle against the Sangragoras.
Just northwest of this area is one last treasure chest which contains two X-Potions. Go north into the next area of the zone as the area east of here is “blocked by a sandstorm”. You will have to fight one last Sangragora that blocks the path.
Continue in to the next area which is Home: the hometown of the Al Bhed.
