It is not enough to bid lowest and offer the shortest deadline for the projects. You need to ensure you are selected by the employer. A good way to do that is to send a private message to the project owner, stating why you are the best candidate to complete their work.
Many people just include general information in the message, and it does not help the employer with making the choice. Your message should be confident, personalized and related to the project.
Do not only state that you are fast, cheap and very good, every other freelancer is going to say that. You can send them information about previous work -similar to theirs- you have completed, and tell them more about your background on that particular field.
You can send related sample work in your private message. But you need to take precautions, as you will never know what they are going to use it for. If you are comfortable, you can send links to your completed sites, projects, feedback on other sites, but never send them anything you have completed for other employers.
If you send a design, you should add a watermark, and if you send articles, state the copyrights in the email. Also add that you are able to create similar projects easily for the employer, too.