Your child will fill your day with many requests. Some may be agreeable to you while the rest may not. Instead of saying an outright ‘No’, try to find and provide alternatives that are acceptable to both of you. With this approach, he understands that you are listening to his request and seriously trying to help out.
Work towards replacing the implausible requests of your child with acceptable alternatives. For instance, your child wants an expensive toy. Rather than saying a direct No, you can tell him, “We will put it on the wish list and find ways to buy the toy. We can work towards saving money to buy the toy."
Another instance can be, your child wants to watch a new movie which has lot of violence. You surely don't want him to watch the movie. You can instead take him for a pizza treat. He may express his desire to draw on the wall. You can explain that this would damage the walls of the house. An alternative can be to provide a white board which also has a black board on the back. In this way, he can do chalk drawings.
This way, your child understands you are on his side and trying to find ways to help him. Gradually, it will strengthen the bond and trust between both of you.