Are Aeris' attacks too weak for your liking?

    During battles, Aeris always starts off in the back row, so her attacks will be less powerful, yet she receives less damage.  However she is not physically very strong, and receives as much damage as the rest of your party.  You can solve her attacking problem by having Aeris equip some Long Range Materia (there is some to be found in the Mythril Mine).  There is also a very good weapon of hers that you can steal from Eligars in the Train Graveyard.  (Use your select button to view the enemy name).  This weapon is the Striking Staff.  It is not her best weapon, but at that point in the game, you will be glad to have it, because her attacks will start to become comparable to the other party members' attacks, even without Long Range Materia... of couse, up to a point...

Are you short of money?

    At the beginning of the game, one problem I always had was getting enough money to buy what I need.  I didn't always want to part with old weapons or armour, and if you don't either, or if even that strategy doesn't get you enough money, then you need to start selling some Ethers.  Ethers ARE necessary in this game, but only after a certain point.  It is possible to win battles without using one MP, so you can save on the Ethers you use.  Also, at the beginning of the game, you will often be faced with a night of rest in a hotel or inn, for a price.  However this price can range from 10Gil to some 400Gil.  You can sell one Ether for 750Gil.  It is very simple to obtain a large number of Ethers.  You can steal them from a number of enemies, even early on in the game.  Some of these are (in order of appearance):
Deenglow -----> Train Graveyard
Levrikon -----> Grasslands Area
Kalm Fang -----> Grasslands Area and area around Kalm
Scrutin Eye -----> Cargo Ship