Final Fantasy X/Mi'ihen Highroad

Mi'ihen Highroad is a long stretch of road leading between Luca and Djose Temple (technically the Temple of Yevon-Djose, but still).

Travelling along the Highroad

Use the Save Sphere up here to save your game and heal up. Make sure you talk to as many people as possible whilst walking along the Highroad, because a lot of them have gifts for Yuna which you can put to good use. Make sure you keep chatting to the scholar guy in front of the statue too, since he has a lot of historical information that you might want to know.

The first battle you come across is predetermined. This introduces armoured enemies - only Kimahri and Auron have weapons with the Piercing auto-ability by default, so only they can inflict sensible damage on them. So, you should leave wolves and lizards to Tidus, aerial enemies to Wakka, elements and flans to Lulu, and armoured enemies to Auron (and Kimahri, to a lesser extent).

Keep walking along the Highroad. The large structure on the left hand side a short way along (which the scholar, Maechen, will talk to you briefly about) has an Ice Brand behind it if you didn't already pick one up. A little further along you'll be introduced to the Chocobo Knights (of which there are only three you ever meet - weird).

There are quite a few different enemies you will encounter on Mi'ihen Highroad compared to that of Besaid or Kilika Woods, and here's a brief explanation of them:

• Mi'ihen Fangs are wolves, so they're magic-resistant and nimble. Their attacks aren't especially powerful or status-heavy, but only Tidus and Wakka can reliably hit them.
• Dual Horns have nasty physical attacks, doing a lot of damage apiece. They aren't armoured or resistant to magic but they have quite a bit of health. You can Lancet these for Fire Breath, too. To defeat them, make sure you inflict darkness with Dark Attack and use Power Break with Auron to reduce its strength. After that just attack it normally.
• Floating Eyes are resistant to magic but won't use any - they have a weird stare attack which hits one person and might confuse them, and a weirder breathing wave attack that hits everyone for similar damage (no confusion, though). One hit from Wakka is enough to kill them, but they will dodge pretty much every other person's attacks.
• Raldos are the same monsters as the one you fought in the piercing weapons predetermined battle - don't bother hitting them with anyone except Auron or Kimahri. They have a ramming attack which can hurt a bit, but otherwise one hit from Auron will kill them.
• White Elements have the same basic properties as the Yellow Elements from Kilika Woods, except their native element is ice, this time. So, use Fire on them. As before, physical attacks do barely anything, and any other element magic is a bad idea (either low damage or absorption).

Anyway, towards the end of the first section of the Highroad, you'll encounter a side section with a lady standing in front of a ruin. Talk to her; she's Belgemine, and will help you train summon usage for related parts of the storyline. You also get a free summon heal before the battle, too.

Fighting Belgemine's Ifrit

Because you're fighting Ifrit you can't summon your own Ifrit, so you can only use Valefor for this battle (quite a big drawback). Your opponent will use attack, Meteor Strike, attack, Meteor Strike in that order, then its overdrive Hellfire once that's full. The on-screen instructions will help you out as well - unless you're going to use Energy Ray, use Shield before Ifrit uses Meteor Strike on you. Don't use normal attacks or Sonic Wings on Ifrit, either, since Valefor's Blizzard will do more damage than either of them and Ifrit is immune to delay. Ultimately it will be no surprise if you don't win this battle - it's rather difficult considering you have no backup aeons and Valefor isn't really that good anyway. You'll get something from it regardless of whether you win or not; a ring for Yuna which isn't especially useful anyway.

Onwards!

Keep heading along the road until you reach the next screen. The chest off to the top from the main road (past one of the elusive Chocobo Knights) contains a Remedy. You'll learn a little more about the perpetuity of Sin further along. If you're a mean and spiteful Tidus as opposed to a good and morally-enriched Tidus, you can kick the little kid's Blitzball away.

The next screen is another long section of road. There's nothing in the first side bit on the left, so keep going, remembering to talk to people for more goodies. One thing you will definitely want to get is a Level 1 Key Sphere from a guy walking around near the right hand side bit further up this section of Mi'ihen Highroad. In that side section there is also a chest containing 2000 Gil.

Further along you'll encounter a chocobo-pulled trailer, and Luzzu and Gatta in a nearby side section. Although they won't reveal much about their plan, a Yevon priestess of sorts, Shelinda, is arguing with a Crusader up ahead and she'll tell you a bit more. Make sure you pick up the 3 Eye Drops in the chest just before the path to the next section.

You'll be outside an Al Bhed inn/shop/travel agency of sorts. You'll enter it and rest. There's quite a long scene ahead of you with Tidus and Yuna.