I am pretty much a beginning sewer. Anjeanette is the one who is much more proficient. Thankfully I have had some time to learn some of her sewing skills. I have come up with a list of decent tips for any beginner.
1. Use measurements and not clothing sizes to purchase patterns. I LOVE browsing the patterns at any sewing store and I am surprised at how many people buy clothing patterns based on their clothing size. THIS WILL NOT WORK! Unfortunately most clothing pattern sizes run SMALLER than our typical retail store sizes. So measure yourself before buying patterns and you will be much happier.
2. Buy patterns on sale. Awhile back I went craft shopping and somehow managed to convince my husband to come along too. He was pretty bored the whole time while I was sitting looking at all the patterns that were on sale for $.99. I picked up 10 to buy and Stephen was shocked that I was going to buy so many when I hardly ever sew (it's true!) but I knew what a great deal I was getting and we went to check out. When the cashier handed me my receipt she joyfully pointed out that I had saved over $100 and had only spent $10, my husband was again shocked.
The point of this story is that patterns can be expensive. Some of the fancy dress patterns I purchased would be $16.99 regularly. Now, unless you are talking about a vintage/specialty pattern, I would suggest NEVER paying full price.
3. A seam ripper is supposed to be your best friend. Even professional seamstresses uses seam rippers...often. Don't be afraid to rip out what you have sewn and to resew it. Plus, this just gives you more times to practice your sewing ;).
4. Buy good quality pins and a pincushion. Pins are so important for holding your fabric together. Even if you are just sewing a straight seam and think the fabric will not slip...think again. Then as your seams become more complex, the pins will become even more valuable.
Pincushions are not just for decoration. As you are sewing, you will need someplace to put the pins you are pulling out from your fabric. Putting them in a box makes it hard to get out one at a time...but a pincushion makes things tons easier.
5. Test your sewing on scrap fabric. Different types of fabrics will require different thread tensions and stitch lengths. Testing out your fabric will prove to be beneficial, and playing around with thread tensions and stitch lengths will help you feel comfortable in your sewing skills.
I hope these tips help you in your sewing endeavors! And let me know of any tips you feel are valuable to pass along to others.