Hey fellow HH players.
This is the most basic hero leveling guide. It may not be the best possible way to level a hero from 1-30 but surely you will find it to be the most efficient way.
In this method you will never replace more than 1 hero in your party at a time. The key point of this is to prevent the newest hero to your party from dying and missing experience. This method also allows you to level a hero safely without requiring defensive items to be wasted on them.
Before you begin you will need one important hero for the front position of your party, this hero will always be in your party and remain at level 30 (or higher). This particular hero is named Queen Sead. She can be obtained easily through the recruit > race by leveling the 5 1-star seedlings. The reason you want this hero (or a similar hero with the same type of skills) is that she has revive (in the event your level 1 dies) and heal. Be sure to make her the party leader so your heroes all get 6% bonus health.
The level 1 hero will always be placed in the back row, in the middle spot. This is the safest spot in the party and it is very rare that your new hero will take any damage in this position. From this point onward you will rotate your heroes as shown in the following picture, removing heroes from the green (front right) location as soon as they hit lvl 30:
You will run level Keronic Base - 1 (normal) until all of your heroes are above level 20, and if none of them has hit level 30 at this point switch to Keronic Base - 9 until someone in your party hits level 30. At that point rotate your heroes as shown above and start back at Keronic Base - 1.
This guide had leveled over 100 heroes this way and have never lost more than 1 wave of experience, and only on a single hero. Even then it will only happen when you get extremely unlucky and your middle back slot gets attacked twice within a very short period of time.
You can feel free to set your game to auto and just let it run.
Have fun and enjoy the game!
Credits: Special thanks to Cavedog for making this guide.