I realized a very useful way to make sure one succeeds a mission: Mission Pets.
You gather up a group of Sylestis, preferable ones high in specific stats.
exmple: strength, intelligence, agility, and dexterity.
If a pet is not high in a specific stats or if u have multiple pets meant for missions required of the above stats, its best to put all lvl up points in health.
*NOTE* remember this are mission pets, not party pets, these guys will not be fighters, but instead doing missions for gold, and AP.
I also found that most green missions are so easy, that a pet can have any stat and complete it, harder missions will need this kinda of info. Reason: ever notice if your party pet, whom norm has mixed stats has a difficult time with harder missions unless they over past the require lvl, it's bc the mission is more likely to succeed the higher a specific stat is. I have at least 5 pets per stat dedicated to missions. This helps greatly with a chance to succeed and as the pets lvl the have not only higher chances of succeeding but you will have a higher chance of completing more missions with a decent number of pets. But don't over do it. I think 5 per stat is a decent number for someone of my current lvl(60). a newbie maybe better off starting with 1 per stat, and adding about 2 new pets once they hit the very hard mark per town, this way you don't have too many and can take on the right amount of missions.
Opinions:
-I believe Armor with the proper stats does increase your chance to succeed a mission, but armor is not needed, and can get pricey, so I would not recommend it especially for a new player.
-I believe proficiencies definitely help with ur chance to succeed in a mission, and unless your have future plans other then breeding and more missions for the pet it is highly recommended to put the proper inefficiencies in, and don't be afraid to go to the next tree.
example: Strength: water, air, earth; as ur pet lvls up every 5 points put their profs into the icon marked as a str increase. Once that's filled go to the next str icon in the other attributes, say you did water first and that's filled you go on to earth/air.
*NOTE* Mission pets can also be breeding pets. I think the only thing these stats may do to the offspring is affect their stats, this is something else that may need to be confirmed.


Questions&Answers&Solidifying Opinions:

I've used mission pets for quite some time now and I definitely recommend it.

Armor can make a big difference I found when going for epic or legendary missions. It's best to have at least that level of gear for those missions I think. These are the missions I do most often when I'm about to go to bed.

I don't know if anyone else has ever had this problem but I've had it a couple times where the first pet in the stable has been selected incorrectly due to lag. I don't know if it's something that could happen still or not or if it's only happened to me, but, out of paranoia, I now leave one starving pet as the first pet in the stable for mission pets. A starving pet can't do missions.

Stables for mission pets can help keep your pets all together so you don't have to hunt them down. My original pets were named after each stat I was going for. I now give titles and then a name instead to newer ones. Titles I use are Adept, Agile, Stout, Strong, and Clever. (I know my Kazuki is neither in that stable nor follows that naming scheme but he was never intended to be a permanent mission pet.)