As my second character is a ranger, I will give my observations gathered from actively raising her.
Medium to long range combat is the name of the game. As you will likely be playing through hundreds of quests with people, when considering who to partner with, look for more physical classes to compliment your ranger. Rangers are fairly squishy, so as soon as you can, pair the class up with something tough like a hunter subclass to improve your survivability. If you have low level armor and or compatible weapons in storage from another character, withdraw it to give yourself an edge. Bosses can punish you hard if you're hanging around them carelessly, so always be vigilant and carry healing items. KO'd characters don't get exp payouts if other players kill the boss while you're out.
Urgent quests should be your top priority, as they will bring in the exp during your first hours of life and even beyond that. A good 12 player lobby can shred a boss on normal in about a minute, which is very desirable because that equals more boss runs. At level 20, you can get access to hard difficulty via Cofy's client order, which will make the exp hauls even bigger. If your main character can spare them, throw an exp boost on before heading in to maximize gains.
Take on straightforward daily/client orders (Kill x boss/Kill y amount of z enemies, etc) to make it easy for yourself. At lower levels, they can help a bunch. Hans and his COs are particularly great for this, and I encourage you to load up on them.
Using this, I was able to reach level 30 with my ranger in about 15ish hours. And that was with taking time to dress up my character, sort out my inventory, and have fun with the game.