Before we get started, let's get 2 facts straight:
1) CP increase is mostly achieved through Grinding mobs with the highest loot level possible
2) Contribution Exp increases by finishing quests

Once your main character finishes its main and side story quests, your Contribution EXP would seem to have come to an end. Fortunately, there are 2 ways around it:
1) Create an alternate character in your family (typically same class as your main so that the alt can just borrow the main character's gears through storage). Finish the main and side story quests. Delete the alternate, and do it again.
2) Go to the Forest of Plunder and do the Eliminate the Goblins repeateable quest

However, these work arounds might slow down the increase of your CP.

Instead of treating CP and Contribution EXP separately, let's put these 2 together:
Step 1:
After finishing your highest Main and Side Story Quest possible, create an alternate character and try to finish the highest Main and Side Story Quest possible as will. Basically, you have to create an alternate character that can keep up with your main and Do Not delete them. It looks something like this:

I know I should've gotten 2 alternate Witches, but I wanted to create other classes to have a first hand experience on how they're played.

Step 2:
Everyday after the server reset and before you grind your monster of preference, accept its NPC Quest (which can only be done once per day after server reset) and its Repeatable Quest. Example below is Ferrid:

Baking a Jar quest in Tarif. Giving you 30 Contribution EXP.


Elimination of the Ferrids in Omar Lava Cave itself. Giving you 50 Contribution EXP.

Step 3:
Complete both accepted quests


Step 4:
After completion, if the Black Spirit asks you about the repeatable quest, choose Stop.

Step 5:
Move to the next type of monsters that would suit your level. For mine, I daily do it with these monsters:
(1) Ferrids, (2) Abandoned Iron Mine Barbarians, (3) Marni Test Subjects, (4) Wandering Rogues, (5) Manes, and (6) Frenzied Skeletons (Eventually after a higher CP, Hasrah Ancient Sentinels)
Keep in mind that Frenzied Skeletons and Hasrah Ancient Sentinels daily quests are not located in Major Towns


Frenzied Skeleton's daily and repeatable quests located in Soldier's Grave


Hasrah Ancient Sentinel's daily and repeatable quests located in Hasrah Ruins Entrance

Step 6:
Since you have alternates that can keep up with your main, switch to them and repeat Step 2. As you can see below, the daily NPC Quests are available again in the alternate charater:

Side Note: The Daily Hand Over Fish Quests can also be repeated once per day by alternate characters

With the 3 characters that I have, I am able to do 1440 Contribution EXP (excluding Camp Quests and Fish Delivery quests). Not bad for continuing the grind and certainly better than staying put and repeating the defeat monsters x1800 which only gives you 50 Contribution EXP each time you complete. On top of that, this method can still be done on AFK, Sleep, and Black Spirit Modes.

This strategy is recommended during Hot Time events. If you're catching up on Contribution EXP, creating an alternate character, progressing its quests, and deleting it is still advisable. I'm actually going to buy my 4th character slot for that purpose.

Once the new maps open, these formidable alternate characters can redo new main and new side story quests in the new maps. The dream is = 5 strong characters and 1 slot for the create, quest, delete alternate character. At this point no need to accept the repeatable quests as doing just the daily NPC quests are profitable enough.