Second, I suggest starting small. If you want to make renaissance clothes, start with a very simple middle class or working class outfit so you can develop your skills before you tackle the more complex upper class costumes. Indeed, you need never go there if you don't like them. Me, I am speaking from over that edge, but I do have different classes and time periods of clothes in my costume closet, and all have their place.
Look at this page: A Basic 16th Century Outfit
Fabrics
A few well made pieces of good fibres will stand you in good stead while you make other projects. Shivering in layers of polyester or sweltering in your satin gown really doesn't make for a happily dressed person. A sweat absorbent layer, a medium weight outside layer and a warm layer for evenings is usually a great place to start. Most working class clothes were layered like this.
If you are making costumes to wear them, think of your own comfort and use the best fabrics you can afford. I buy a lot of my fabrics from thrift stores and from discount fabric places or ethnic suppliers where they are cheaper. Also, buy really good thread. You don't want to have it all come apart. This means all cotton or mercerized cotton but likely not polyester.
Elizabethan Layers
People often ask me what is it I am wearing when I am in full Elizabethan. This website at Raveness has a good overview of the garment layers, and how it differed by the person's class. It uses women's clothes as the main examples, but its got valid information for men's too. http://www.raveness.com/costuming/renaissance/index.html
Resources in Costuming
The mother of all elizabethan costuming sites is this one, the elizabethan costuming site Start here on your journey.
It has stuff from different cultures, notably, her good research on Flemish peasant, and links to Bella of Verona's venetian research.
One of the areas I did some research and experimentation on this last few years was fitted 14th century women's clothes. There is a link to resources on this at the foot of the page.
Pattern Drafting
Drafting your own patterns can seem a bit daunitng but trust me, it does work well once you have the hang of it.
There's good instructions on the Elizabethan Costuming site, and
at Marquessa Laurellyn's site, the Renaissance Tailor at http://www.vertetsable.com/. It works best with a friend to help you, and you need a tape measure, pins, tailors chalk or white soap if you are using dark fabric or pencil on white.
If you aren't ready to go there just yet, there are good commercial paper patterns out there for 16th century clothes. I have used Margo Anderson's ones with a fair bit of success, as long as you fit them to the body you are working on. Margo also has a very active Yahoo group for users of her patterns; folks on there will help answer questions.
Others also recommend Kass McGann's patterns at Reconstructing History, which is a very good website but has been down a bit lately..
Costuming Links
For a good source of web links, the costumer's manifesto is a great place to start, at http://www.costumes.org/ and then I use the costumes sorted by history link http://www.costumes.org/history/100pages/costhistpage.htm.
Inspiration and First Hand Sources- Portraits:
To see many people's finished garments, you can review the Featured Attyre pages, at http://homepage.mac.com/festive_attyre/feature/feature.html and its archive. Lovely to see people's work and get to appreciate it.
Look at the real thing in museums or in webgalleries such as http://www.wga.hu/index.html. Costumers love glossy books with great clear colour pictures of paintings. Bless those painters who put in the seam lines and the stitching details so we can learn more.
Fitting Your Garment:
See the Sempstress' website at http://www.sempstress.org/ to understand what the different wrinkles are telling you about the fit of the garment.
Other Time Periods
15th Century
There's great resouces on pretty much every time period out there. I like the articles on fabrics at this website of Cynthia Virtue's, http://www.virtue.to/articles/and her guide to clothing quality for bachelors. Her site concentrates on the 15th century but its quite interesting.
14th Century
There's good info out there on the 14th century gothic fitted dress too, which I have gathered on this page. Note: I don't own any of the resources and their respective authors retain all copyright.