Regular materia does not matter in which slot you put it, you can put long range in your armor and still benefit from the long range materia in the same manner as if you had put it in your weapon. However, and i'm sure you know since you think of yourself as a expert, you have combine or support materia where you need to put it in a linked slot with a combination that works. Like "All&ICE" that let's you cast ice on all monsters on the field. Elemental materia does matter if you put it on armor or weapon, it can add elemental damage to your attacks or extra resistance to it when you put it in an armor.
Then you also have equipment that has an effect on the materia it holds, like double XP or none. So if you want to level your materia faster you should wear one of the double XP equipment.
The following is a list of some good combinations i fetched from www.uffsite.net
Added Effect + Contain
Weapon: Attacks can cause a number of status effects such as Petrify, Confuse, Berserk or sometimes Paralyze to one or more enemies.
Armor: User becomes immune to Petrify, Confuse, Berserk and Paralysis.
Added Effect + Destruct
Weapon: If you're lucky, the weapon will deal a death-strike.
Armor: User becomes immune to instant death attacks like cross-scissor.
Added Effect + Mystify
Weapon: Some attacks can cause Berserk or Confuse to an opponent. If it's the former, then that's not too good. However, the power of confusion is very handy to have.
Armor: Gives the user immunity to berserk and confused statuses.
Added Effect + Poison
Weapon: Some attacks can poison an enemy.
Armor: User becomes immune to poinson attacks.
Added Effect + Seal
Weapon: Gives a very good chance of silencing or putting an enemy to sleep.
Armor: Grants the user immunity to Silence and Sleep.
Added Effect + Time
Weapon: Some attacks slow or even paralyze the enemy.
Armor: Gives the user immunity to Slow and Paralysis.
Added Effect + Transform
Weapon: Some attacks inflict Mini or Frog on the enemy.
Armor: Gives user immunity to Mini and Frog status.
Elemental + Elemental Summon (Ifrit, Shiva, Titan...)
Weapon: Adds element of summon (Fire for Ifrit, etc.) to weapon.
Armor: Grants user 50% resistance to summon element (resistance to Ice with Shiva, etc.).
Pre-Emptive + Materia
Anywhere: Depending on how lucky you are and how levelled your pre-emptive materia is, you'll sneak on the enemy(ies) and use the action associated with the linked materia.
Final Attack + Anything
Before your character dies, he / she / it will perform the action associated with the linked materia. For example:
Final Attack + Revive
Anywhere: The most basic combo for your character's dying act - He / she / it will cast the Revive spell on themselves right before dying.
HP Absorb + Damage Dealing Materia
Anywhere: The linked materia attack will restore some of your HP. For example:
HP Absorb + Knights of the Round
Anywhere: When KoTR attacks the enemy and they die (because they will), you will gain a lot of HP from it.
MP Absorb + Damage Dealing Materia
Anywhere: Same as HP Absorb + Anything, except it restores MP and not HP.
MP Turbo + Materia
Anywhere: This will use more MP to make the attached materia more powerful. For example:
MP Turbo + Knights of the Round
Anywhere: If your Magic stats is pretty high, this will cause each knight to deal up to 9999 damage. This means 130,000+ damage altogether.
Quadra Magic + Materia
Anywhere: The attached magic or summon materia is performed four times for the cost of one, but does half damage with each casting.
Counter + Deathblow
Anywhere: Counter attacks with a deathblow to that enemy.
Counter + Manipulate
Anywhere: Counter attacks by manipulating the attacking enemy.
Counter + Steal
Anywhere: Counter attacks by stealing from the enemy.
Counter + Morph
Anywhere: Counter attacks by trying to morph the enemy into an item.