Leaving comments on a other people blog can be source of traffic to your blog. You can also get back link, if they are do follow blog. By posting a controversial comment, you might have lots of traffic. Here are comments tips so you get maximum result:

• What is you target on commenting? Is it SEO reason or is it branding your self. If you want to brand your self, it is better to use your own name instead of using your keyword. When you use your name, people will remember you more easily. If you have common name, change your name just like celebrity change their name. If you want back link, you should check their page source code. Search the source for 'nofollow'. If it exist, then you will not have back link to your blog.
• Make a good comment, which is clear, and relevant. Make your comment usefull for other people reading it. Dont just say Good post". Write why it is good?
• Try to be the top commentators, because it will bring you many traffic. You will get link from their home page.
• Choose your words wisely. You don't want to create trouble that could make someone hate you. It is good to write constructive criticism that doesn’t hurt others feelings.
• Be the first commentator. People usually pay more attention to first poster.
• Do not put your signature in your comment. I think it is unnecessary. Your post usually have your name in titlelink. So don't be greedy.