|These NYC area players look ready to rally!|
Pair players up. One of the pair self-rallies a certain number of times. How many times this is can be set by the coach or determined by some other fun method such as rolling a dice, picking a playing card, etc. After the player completes their number of self rallies, they bump it to their partner (a true rally) and the partner repeats the process.
Easiest - low number for self rally, no net between partners
Harder - increase number of rallies; add net as barrier between partners. For even more of a challenge, shrink the court and have them play only in a service box or only in an alley.
Adapted from USTA's QuickStart Tennis guide