Biggest piece of advice, start with Wandering Palace and just explain that you're new to 50 and open to tips. Research ahead of time so you have an idea of what to expect and look for members who can help you. If the group is full of elitists who resent that you're new to 50 and don't want to help out, drop group. The 15 minute cooldown on Duty Finder isn't that bad and maybe you get into a better group the next time.

At 50 I've had groups that were helpful and ones that resented the fact that I hit 50 earlier this week and didn't know every tiny nuance of the level 50 instances. Ignore the latter and you'll be fine. With good group members who are willing to help out, you'll do ok and there are plenty out there who will be understanding.

Beyond that, what other people have said. Run Ifrit for the weapon (you'll like be on shield bash duty anyway). Run WP for points and buy the cheap DL gear (belt, gloves and so on) first. You'll be fine. Good luck.