How many times in the past month have you agreed to do something when you don't really want to do it? We all do it at sometime or other and we should learn to say "No"if we do not want to do it.
Why should other people think that your time is not precious to you? Saying no in the workplace is a slightly different matter but saying no to friends and family should be done without guilt. You need to learn to value yourself and what you do.
We are all given 24 hours in a day and for a certain percentage of that time we should be able to choose what to do with it. No one has a right to think they can control your time if they are not prepared to give up some of their time too.
If you have some free time then it is because you have planned your activities with care to ensure that you have time to do what you want to do or that you have chosen to give yourself "me" time. In agreeing to do a job for someone else you lose that free time.
One way of dealing with this is to agree to do a job for someone if they will do a specified job for you in return. At first they may be shocked that you have asked them to do something but why should they be shocked?
After all they have encroached on your free time so why shouldn't you encroach on theirs? If you share a house with others then you need to share the up keep of the house too.
If you are a stay at home mum or dad it does not give your partner the right to be in control of your time either whilst they are in or out of the home. State in a calm but assertive voice that you need to have free time too and that, in order for both of you to be able to things you enjoy, a rota for jobs should be devised or that you each have a set night off.
Just because your job is at home does not mean you should be on duty 24 hours a day. Decide what goals you would like to achieve outside the realms of running a household and workout how much time you would like to spend on them each week.
If each member of the family also does this and then these goals are shared as a family it should be possible to make sure everyone has some free time and others need to respect this time and not take offence when other family members are not able to do extra jobs.
As you learn to say "No" once it becomes easier the next time. Push the guilt to one side and pay attention to what other emotions you are feeling besides the guilt when you say "No".
These are the emotions that you need to deal with first. They could be resentment, lack of self worth, irritation or even panic that in agreeing to do something for someone you will not get your own jobs done that are important to very day life or working to your goals.
If guilt cannot be pushed to one side then work out why you feel guilty and why it is difficult to say "No". Do you feel you lack the communication skills to say "No" without offending people?
If so then take a course on communication skills. Do you feel that your time is also valuable but that others will not see it as so? If this is the case then do a thought shower as to why your time IS valuable.
This is for your eyes only. You do not have to justify yourself to anyone. It should be enough for others that if you could do it you would and the fact that you have said "No" means that your time is needed elsewhere.