There's yet another problem with vintage patterns. Many of the earliest patterns are perforated rather than printed on the paper, meaning that it becomes necessary to basically guess how the pattern pieces go together based on the perforated holes. This problem can be averted in the future by first tracing the pattern onto tracing paper and writing notes on the pattern pieces for future reference.
If you're new to sewing, get yourself a basic sewing manual before attempting a vintage pattern. I like The Sewing Bible: A Modern Manual of Practical and Decorative Sewing Techniques or even Reader's Digest Complete Guide to Sewing, but you may have your own preference. If you can find an older sewing book, you will have a greater chance of deciphering vintage techniques. Even an experienced seamstress may benefit from having a book around to help explain unusual construction techniques, such as gussets, that can be found in vintage patterns.
When you're looking for vintage patterns, try to avoid those created by well-known designers. They're incredibly complicated and difficult to complete even for an experienced sewer. Instead, look for patterns by Butterick or Simplicity which are marked "Quick" or "Easy." These will typically be easier to complete than more complex patterns.
If you purchase a pattern and find it has missing or damaged pieces of instructions, try Pattern Rescue. This site is dedicated to preserving and restoring vintage sewing patterns and can be a great resource for anyone having difficulties with vintage sewing patterns.