Efficient Raid Soul Spending

Raid souls is one of the most important resources in the game and spending the raid souls you do manage to acquire efficiently will increase your progression rate exponentially.

 Early Game 

Focus on getting all heroes to 90% defence to reduce cost.

Work on gaining all the upgrades. Excalibur > Merlin > Camelot > Round Table > Holy Grail

 Mid Game 

Once you have all the upgrades unlocked, it's time to start building up your heroes. Focus on getting all heroes attack up so you have the 600-1000 skill upgrades unlocked.

Fire Arrow also has a use. It is not as strong as you might think however. I'd recommend leaving your fire arrow at approximately half of your RT level. So RT = 10, FA = 5.

 Late Game 

Okay this is when it starts to get interesting. You've maxed all your upgrades, you're starting to level your Round Table, your Fire Arrow and your Heroes. How do you spend the points efficiently?

So, as said previously i'd recommend you have your Fire Arrow (FA) at half the level of your Round Table (RT).

As for the hero levels...this is where a bit of math comes in handy!

So the optimal ratio of RT to heroes is as follows

=1 / ((((RT+1)^5) - RT^5) / RT^5) * RT * 2000 / 16

Confusing? I know. So here's a few examples.

Let's say your RT level is 10. If you plug that into the formula the answer is displayed as 2047.46851. Round that to 2047.

So if you're RT is 10, you want to aim for all your heroes to have an average level of around 2047.

So when do you upgrade? Let's plug in 11 and see! 11 comes to 2522 hero level. So get your heroes to an average of 2522, then upgrade. Then 12 is 3047, rinse and repeat.

Some quick fire reference points: Link To Spreadsheet Calculator