If you grew up with siblings then I am almost one hundred percent sure that at one point or another you had to use the power of persuasion to get something that you needed done or make sure that everyone is getting along in the house hold like they should be.
To some this may seem like a no brainer, to others, this can be one of the hardest things in the world, the key is to stay calm, do not become upset or show any negative emotions, even if something is not going the way you want it to, just stay relaxed, take deep breaths and keep your mind fresh and clear.
Make sure that you use something as motivation, such as something that you know for a fact that they cannot resist.
Tell them that if they do this special something for you, that you will in return give them something, this is the best way to deal with someone you know, the reason is, most friends and family will not take money from you for doing a task anyway, the mind thinks that it is wrong and they will feel guilty, you do not want to make them feel guilty, in fact, the goal is to make sure that they are excited about doing this favor for you.
For example, let us say that you want your little brother to clean the kitchen, instead of yelling and causing a big scene about it, calming approach them in a open and friendly manner, make a joke to break the ice or ask them if they are currently doing something, if they say yes, take a small moment to ask about their current project, then say, hey, if you get a chance could you please clean the kitchen?
I will take you out to get something to eat afterwards, it is my treat, I am ready when ever you are, once everything that needs to be done is finished.
Making the other person feel like they are gaining something will make them more willing to think about what is being offered, although that does not mean that the other person will automatically jump on the deal, more than likely they are going to evaluate the situation and see if they are in fact getting a good deal, if they do not seem interested with your first offer, it never hurts to increase what you are willing to give back to them in return for their hard work.
When you are dealing with persuading family and friends it can be the easiest task ever, because you already know what they love and hate, it will also give you an emotional upper hand because this person has invested feelings into you which nine out of ten times will be the only motivation they need, but in other cases, the key is to continue talking and prying until they say yes, try approaching the situation from different angles, try different offers, make sure that you are making this sound like the best thing in the entire world, because in order to be persuasive you have to make them think that it is the best thing in the world.