How do you come across in your emails?
As I receive more and more requests for assistance by email, I also get more and more poorly worded or badly formatted emails.
When you ask someone for help, or approach them for the first time, you will get a much better response if you word your initial contact carefully. Take some time to think about what you want from the other person.
Be descriptive, many people have a lot of things on the go at once. You may know exactly which piece of software you just bought which didn't work, but if the seller has 20 products, an email saying "I couldn't download the software" will sit on the to do pile longer than one which states which software you bought, and what happened when you tried to download it.
DON'T USE ALL CAPITALS in an email, it is considered shouting and also looks a tad unprofessional if it is your initial contact with someone who you may wish to do business with at a later date.
Don't demand action, request it, this is even more important if you are asking for help or you are referring to something which was free in the first instance. You may think that would be obvious, but I have personal experience of people demanding action be taken when something free didn't work. A simple description of your problem, and a "please advise" will get you much better results much faster too.
Formatting your emails can also help enormously. Putting in your own line breaks (using the enter key) at around 60 characters or so will make your email easier to read.
Add some contact information at the bottom too. It's much nicer to receive a reply from someone using your own name, rather than just a dear sir at the beginning, and you will get more personal service if people at the other end of your emails know your name. I personally like to send emails to a person not just their email address.
These may seem like common sense to you, but take a little time to see if you're missing any of these little points. Your email is a communication as much as if you were face to face with someone. Make sure they get the impression of you, that you'd want them to have.