It would be great if players could enter "practice mode," similar to edit mode. Allowing the player to attack his/her base at it's current layout, selecting any combination of troops at the highest level the player has previously unlocked.The amount of troops the player should be able to carry to practice mode should correspond to the player's army camps. Also creating troops for practice mode shouldn't cost any resources or have queue time.
Practice mode would enable the player to find the weaknesses in his/her base so that he/she could edit his/her base accordingly. Also allowing the player to practice attacking bases that are similar level as his/her own. As a result, player's skill levels and attack/defensive strategies would be better, making CoC a bit more competitive, therefore more fun. Practice mode would also allow new players the opportunity to get a grasp for the game more quickly; decreasing the amount of new players quickly abandoning their accounts from becoming discouraged.
This has been requested many times and rejected every time. An open mode like this is WAY to easy to exploit. I have another thread with a similar idea but much more restricted to how and when it can be used so exploits are prevented. Unless you have a truly original idea SC has already given a flat NO answer to this, and it is the correct answer.