First, you need to believe that your memory is good. If you keep telling yourself that you have a poor memory, then you will continue to have a bad memory.
After that, it depends on what you need to improve about your memory. Names? There are lots of tips and tricks for remembering people's names, such as picturing their name by its sound and associating the sound with the visual of their face, or repeating the name as soon as you hear it and using it several times when speaking to them.
Maybe you need to improve your memory for learning for exams? Use mind maps from Tony Buzan. Create a mind map of all your subjects, using lots of colour and mnemonics and little icon pictures. That will help you remember.
Dates, meetings, appointments? Get a good big calendar, stick it up where you will see it every day and put a reminder on your phone or coputer to check te calendar every night before you go to bed (so you can prepare for tomorrow) and every morning when you get up. Train yourself to complete your calendar every time you have a new appointment.