You can keep these points in mind:
1 Communicate effectively . Read the project description carefully and thoroughly. Give importance to the requirements and post a reply( or Bid/Quote) only if you are 100% sure that you can do this work comfortably.
2 No Standard replies . Don’t post standard template based replies. Your Reply should be specific to the given project.
3. Create a Professional portfolio document (if you are not allowed to share your contact details otherwise create a website and provide the link) and provide it to the client, only if they ask for it.
4. Your reply should contain the reasons, why client should choose you, So, write your strong points first. Be truthful and honest.
5. If you are new to freelancing, try to get small project first to get initial positive reviews and ratings.
6. Try to work on some personal project or some open source project, mention this in your Portfolio.
7. Be an expert in your work domain. Instead of working on 100 Technologies, better develop expertise for some specific technology and work in that.
Best of Luck!