Well, people can correct me if I'm wrong, but vibrato is something that develops/gets stronger as you grow older and your voice matures. You really can't force a vibrato. IMO, you can cultivate and help your vibrato grow, but you can't "make" a natural vibrato. And as far as strengthening your voice, singing scales and good warm-ups every day will help to do that. When you warm up, you should stretch and make sure your body is loose so nothing is tense when you sing. I also find it is important to start with something "light" when you warm up, and then slowly work into your belt. Strengthening takes time, effort, lotsa patience, and care.
Also, you should not sing every day if you're not singing properly. Before you start singing, just work on breathing. Take in a big breath and slowly blow air out while counting to 30. This helps breath control. Make sure you don't feel any tension in your throat. Another way to relax is to form nice round vowels when warming up.
If you really feel you aren't singing properly though, you best make room in your schedule to see someone for lessons, as us on the forum can't see you when you sing so we can't always give the best advice.
Best of luck to you!
Posted on Mar 6, 2008, 1:57 PM from IP address 184.108.40.206