You want to consider what PT you need to train. So I'm going to list the important stuff and why you'll need to train them. I recommend only training addition combat PT's just enough for the next level of equipment.
What each PT does:
All combat PT effects the accuracy of your attack. For example a player with 37 ranged PT can hit a lvl 50 mob with a lvl 30 weapon quite succesfully while a player with 20 PT will miss almost all of the time on a lvl 50 mob. (Tested and confirmed.)
Melee: Increases SP and attack damage with melee weapons.
Ranged: Increases SP and attack damage with ranged weapons. Ranged also increases evasion (tested and confirmed).
Force: Increases FP and attack damage with force spells.
Defense: Increases HP as well as resistance to attacks.
Shield: Increases chance to succesfully block an attack while equipped with a shield.
SUMMON: (Summoners only) Allows you to control higher level summons. Also increases Inanna heals and summons damage (Tested and Confirmed).
All Classes
Defense PT: This is always nice to have as it increases your HP as well as increases your resist.
TIP: Close Range Armor and Shields are helpful in training defense at a lower cost.
Make sure to at least get the sacrafice darkness buff.
Caster/Warlock
Force PT: (Required) This is your main PT and the one you excel in. On top of your PT you have force tier pt as well. You can see your force pt by hitting F or ctrl + F. You want to try and level all 4 elemental offensive spells at the same time. So get your other two offensive spells and your darkness buffs and sacrafice asap.
Ranged PT: (Recommended) Ranged PT increases stamina. You'll need stamina for your class specific buff and not to mention it helps on those long runs.
TIP: Dark Force PT can be a pain to get to 30. A nice tip is to switch the Sacrafice force reaver to a level 1 each time the reaver reaches level 3. You also want to use both Dark Force buffs as much as possibe as soon as possible.
Summoner/Grazier
Force PT: (Required) This is your main PT and the one you excel in. On top of your PT you have force tier pt as well. You can see your force pt by hitting F or ctrl + F. You want to try and level all 4 elemental offensive spells at the same time. So get your other two offensive spells and your darkness buffs and sacrafice asap.
Melee PT: (Recommended) This will help when you need to tank for your summons as well as give you a boost on that defense PT.
Shield PT: (Recommended) You can train this as you train melee. This will help cut down on damage taken as well as HP Pot cost as you tank for your summons.
Ranged PT: (Optional) As said before it does increase Stamina by 10 per PT.
TIP: Dark Force PT can be a pain to get to 30. A nice tip is to switch the Sacrafice force reaver to a level 1 each time the reaver reaches level 3. You also want to use both Dark Force buffs as much as possibe as soon as possible.
Warrior/Champion/Guardian
Melee PT: (Required) This is your primary PT, so train it first. You can cap it pretty fast and have time to train other PT before you level. Make sure to keep an eye on the Melee Skills PT. You want to get the 2nd tier by the time you ding 30. I keep an eye on my PT at all times and set a goal for each PT per level so that I don't neglect my main PT and get it to par by lvl 30. I use a one hander so that I can get the max Melee Skill PT per level.
Shield PT: (Recommended) Shields add to defense as well as blocks attacks. Shields even block magic.
Ranged PT: (Recommended) Train this if you melee PT gets capped. You can actually train this and shield at the same time by using throwing knives. However I recommend a ranged weapon as you can train this PT up in a matter of minutes due to the lower cap for warrior based classes. Ranged does three things, it allows you to wear ranger armor which has high elemental resist, increased attack speed and it increases SP. The ranger armor is nice to have when fighting mages.
Force PT: (Optional) You will have little time to train force since melee skills PT requires alot of time. However it's still possible if you feel all of your PT is at a comfortable level and want to level a little faster. Force also increases FP which can be a nice addition to a low FP class.
Warrior/Knight/Black Knight
Melee PT: (Required) This is your primary PT, so train it first. You can cap it pretty fast and have time to train other PT before you level. Make sure to keep an eye on the Melee Skills PT. You want to get the 2nd tier by the time you ding 30. I keep an eye on my PT at all times and set a goal for each PT per level so that I don't neglect my main PT and get it to par by lvl 30. I use a one hander so that I can get the max Melee Skill PT per level.
Shield PT: (Required) Shields add to defense as well as blocks attacks. Shields even block magic.
Ranged PT: (Recommended) Train this if your melee PT gets capped. You can actually train this and shield at the same time by using throwing knives. However I recommend a ranged weapon as you can train this PT up in a matter of minutes due to the lower cap for warrior based classes. Ranged does three things, it allows you to wear ranger armor which has high elemental resist, increased attack speed and it increases SP. The ranger armor is nice to have when fighting mages.
Force PT: (Optional) You will have little time to train force since melee skills PT requires alot of time. However it's still possible if you feel all of your PT is at a comfortable level and want to level a little faster. Force also increases FP which can be a nice addition to a low FP class.
Rangers
Ranged PT: (Required) Ranged does several things, it allows you to wear ranger armor which has high elemental resist, increased attack speed, increased run speed and it increases SP.
Melee PT: (Optional) Melee also increases SP at a lower rate. However it's nice to have a back up fighting method if you run out of ammo.
Force PT: (Optional) You will have little time to train force since ranged skills PT requires alot of time. However it's still possible if you feel all of your PT is at a comfortable level and want to level a little faster. Force also increases FP which can be a nice addition to a low FP class.
Specialist
I actually recommend training all PT's for this class since it has lower caps and shouldn't have much trouble training them all. This class only has access to Tier 1 skills and spells so versatility in all PT can be a great advantage to this class.
Ranged PT: (Recommended) Ranged does three things, it allows you to wear ranger armor which has high elemental resist, increased attack speed and it increases SP. The Sp is important to specialist because they require a large amount of SP to do their revive skill after 40.
Force: (Recommended) I recommend force for this class simply because the AOE spells can be an easy way to farm for those crafting mats off of lower level mobs.
Nothing specific other than the above about these guys. They have lower PT caps since they do not specialize in one specific damage type so all thei caps are average. You actually have time to train all of your PT to cap each level. So just watch your PT closely and get the most PT training per level. Before lvl 30 you'll actually cap all of your PT before you even get to the next level. You can use that time to PL using force or in a group.
If you do not cap your PT per each level before 30, you will not be able to equip the next level of gear on a specialist.
