When I started playing RO, maybe 10 years ago, my first job was a swordsman class. Some 10 years later, I prefer long-range attackers since I could last longer in a PvM fight by putting a distance.
Basically, it helps to understand the pros and cons of a certain job class. First Step I think is figuring out whether you prefer close combat vs long-range combat.
Second Step Once you have chosen your preferred fighting style, next is understanding the simplicity or the complexity of the job class skill. A good example are the mages, they have tons of elemental skills and I think you need to sift through the "must-haves". You can also gain some other skills outside your job class through weapons or cards.
Third Step Understanding which stats would go well with your job. DEX works well for long-range combatants as well as for skills with a lot of loading time (because high DEX makes loading faster). Aside from leveling up, you can also increase your stats via cards and gears.
To be able to maximise your skill points, it is best to level up your JOB LEVEL to 50 before changing to 2nd class.
It helps to create a merchant class so you can get the OVERCHARGE skill. As the name implies, you can overcharge your loots to NPCs and in doing so, earn more zenny.
Best place for archer class (Double-Strafe), acolyte class (Heal), and mage class (Soul Strike or Fire Wall) to level up crazy quick is at Glasheim Churchyard or Glasheim Prison. The rest, you may search on TRO forum, TRO wiki, or Google.
AND some gears, equipment, and weapons, although the same, may have different prices because:
1. Players sell them and they have their own selling price as there really is no standard price.
2. Some of these gears, equipment, and weapons have been refined (+1-+10), have card slots as well as have cards slotted in it (the rarer or more special the cards are, the more expensive they are).
3. Have elements forged into it.
4. NPC buyable gears, equipment, and weapons are of course more affordable.
Disclaimer: I am no expert on the game itself but these are just things I have picked up over the course of my on and off gaming life. The rest of it is yours to find out. There are several guides offered on Talon Wiki, mostly QUEST guides, etc.
I hope I got to help because this is probably the 3rd time I ventured outside my usual forum topic. Lol.