We must start from the simple - become aware of a problem. Without this it will be impossible to change the situation. Try to understand how your relationships are unselfish. If we analyze, we can easily see the motives that moved by your friend, loved one or colleague.
Try to identify the moments that seem suspicious, and then gently and tactfully refuse a loved one in any detail. Then watch his reaction. If a person does not pay much attention to the incident, your relationship is not threatened. But if people show their resentment and try again to get something from you, better to tune in for an early break in relations - people will realize that you have nothing to take, and you will cease to apply.
With colleagues, the situation is a bit more complicated, as fellow parasites are quite capable of breaking your life. Refusing they need even softer and unobtrusively as possible. The first time you say that in a hurry to submit the report and simply do not have time to help, at other times with the most serious kind report the important meeting. Whenever keep tactfully but steadily "bend the line". The main thing - in any case do not let them know a colleague that you know all about its consumer intentions. Believe me, this parasite itself retires after a while, because you will lose all value in his eyes.
Say the first time sweet and friendly person "no" is always difficult, but doing it once, the next time will be easier to refuse. Watching the man for some time, you will clearly understand who is in front of you and what you need from him.