CB channels are mutually shared among many users. Interruptions and conflicting transmissions from multiple users on a channel can make it difficult for your intended recipient to understand your message. To make sure that your transmission is received well, and as a courtesy to others, wait until the channel is clear before pressing the PTT switch.
If too many users are actively using a channel, try to specify another possible channel to your intended recipients so you can resume your conversation together on that channel.
For important communications, make sure that your recipient acknowledges that they have received and understand your message.