So, I just got my very first Gold Mars Coin by activating SpotPass for the game. I had to boot my game, check My Room's Plaza, read the message and tapped the Gold Coin button. I'll keep that coin, as I don't know where I should spend it first.
Also, I managed to reach Master Rank on both Solider and Mercenary on Level 32 to 35. The tasks aren't very hard, but it takes a while to complete them all. Apparently, each Master will hold a party once you reach the Master rank, and each have their own different music. There's a couple more ranks to reach, which is Hero, and then Legend (if you manage to clear every task for that job).
For any battle involving with T-Rex or Dragon, it's a good idea to stock up with tonnes of healing items, items that restore your stamina point and revive potions. One fight that one red dragon lasted me one in-game day (around 20-30 minutes), and consumed many stamina potions and high cure potions.
Figuring out on when to dodge and when to attack helped me a lot, so you should put this tatic in practice. When they spit magic, they leave you a good opening for you guys to strike with a charged attack or a special attack (when your tension gauge is at max). That way, you'd take much less damage. Oh, and dragons can summon a temporary magic rain around them when their HP bar is halfway cut. Just don't act like Leeroy Jenkins, and you'll end up fine.
I recommend you guys to pair up with NPCs if you don't feel like finding players online, In this case, I got Yueria and Isabelle to my party, and they both do a good job helping me, especially when the relationship is high. When one of them die, I always had to revive one because the other AI-controlled NPC is too busy handling the fight. At least, you get more time for you to prepare your next move when a boss is focusing on the NPCs.