It all starts in Midgar. In this place you will have to set a bomb to blow the reactor. The main goal here is to beat the first boss. There is no need to train here. All you have to do is to go with Cloud to the battle place as fast as you can. Most enemies can be killed with just one blow. Don't run away from battles, the time you wast waiting for the escape can be better used to fight them instead. Once the boss battle begins attack with with nothing but physical attacks ONLY! Magic attacks animation are just too slow to make them "time profitable". In the same time you can attack two or three times with the sword and the gun. Limits are a bless here. Once the tail goes up, stop attacking and cure yourself. I know it's a waste of time but it's neccessary.
Phase one clear.
Now along the way you will meet tifa and you will have access to more powerful guns and some materia. Don't waste time and money buying such things. Not only magical materia will lower your HP but it will also reduce your attacks force. Equip only the Cure materia with All on Cloud for bosses. Along the way you can equip on Cloud Bolt+All to clear the enemies instantly.
The second boss is the one you fight with Cloud, Tifa and Barret. He is weak to Bolt but you can make much more damage with attacks. Use the limit only when he is turned back to you! This one is too easy...
Now Cloud is having a good time with Aeris and they both will have to fight some pals. Bolt+All still kills them instantly. The next boss is the one you fight with Cloud and Tifa and Aeris in the sweepers. This one is hard so you need to attack as fast as you can. Forget about magic for bosses, it's too slow... Don't forget to steal the powerful sword for Cloud in the Shinra Building. It's the guys with big swords. They are very dangerous!
I will jump the guide quickly to outside Midgar because strategies don't change that much untill this place.
Once you leave midgar take with you Cloud, Aeris and Red.
Don't buy anything. Just keep going. Forget about chocobos for the Cobra. You can pass it with skills and good timing.
Now that you reached the Fort Condor forget about Yuffie too. She is too weak.
Now for all the bosses don't forget to use Bio attack to make to poison them. This way the "poor" creature will lose a lot of health by itself. There are no Big and Bad bosses you can't beat in the first meet if you follow this guide.
Now for Barret Boss use nothing but physical attacks and cure. Don't train any materia. They are not worth it. They only make you weaker.
The next big shot is the Cosmo Cayon Boss. Before going to meet this pal you need to learn the Aqualung Skill in the desert By now you should have 2 or 3 Enemy Skills. These skills are the best of the entire game since they use very little magic to make devastating damage! You should learn Aqualung, Big Guard from Cosmo Cayon area beach enemiesm the ones with tentacles, you need to manipulate them. Also learn the White Wind skill from the Fort Condor area. Now you are virtually invencible. For the Cosmo Cayone monster just feed him a X-Potion and he will go straight to heaven.
Toss all the materias now except Enemy Skill. If you want to wipeout any random enconter Aqualung will do fine. For the next Big Boss you will need to attack him with Aqualung and physical attacks only. Palmer is another easy one. Now in the Temple of the Ancients Aqualung will wipeout anything you want. Forget about any kind of Summon. It's just not worth the time and the MP. Keep in mind that weapons also give you some extra status they DON'T SHOW! If you don't believe change one sword or two for Cloud and see the change in his Vitality and Magic!
Now that you lost Aeris it's time to use nothing but Cloud, Cid and Red. Aqualung from now one will not be enough for the beasts that are going to come. Too bad there is nothing good so far. Keep attacking with physical attacks and curing yourself. Once you can learn Magic Breath you are automatically done. This is one of the best attacks you can ever learn! Too bad it's only useful to wipeout random enemies as the bosses absorb it!
So far you should have Equipped:
Cloud - Enemy Skill and Death Blow + Added Cut and Alexander + Mp Turbo.
Cid - Enemy Skill and Counter Attack and Cover! So you can counter attack more often and Bahamut.
Red - Enemy Skill + Kujata
Use the summons only when the enemy is Near Death because it's when they become angrier and they show their true faces!
Now cloud is sick and you need an extra character. Barret will do fine. Just keep attacking the enemies with the previous set and you will do fine all the time. The curse ring can be a great help for random enemies as they boost your status and you leave the battle soon enough.
The next big Bosses will be Rude and Reno and Elena and of course the Proud Clod. They all have a lot of HP but weak attacks. Counter Attack and some other physical attacks will do fine.
On the third CD you can continue to use only physical attacks, no problem.
The final bosses are just too easy to be called final bosses.
Just keep in mind that the most important thing are the attacks that are very fast and nothing can beat physical attacks in terms of time/damage.