A long time ago, there used to be a term 'the authority of print' and people really did believe what they read in the the newspapers. Nowadays there have been enough newspaper scandals to convince the general public that things are not always what they seem. My personal watershed came when I was working on a Sunday paper during the first Gulf war and there was a frantic search for 'an expert' to comment on what was then an unprecedented situation. TV news, with the publicly exposed different coverage of various US channels in particular, has lost a lot of its weight. Possibly radio, particularly the BBC world service, retains some credibility, but blogs? Most of them are way, way down the information feeding chain.
However our thirst for information is greater today than ever. Information has become more tradable than a spy's whisper during the Cold War. There's a huge daunting body of facts out there that for many people is simply overwhelming. So first of all when you're establishing a professional blog of any kind endeavor to the best of your ability to ensure that at your time of writing any facts are accurate and any opinions you offer are founded on reasonable research. It doesn't matter if your blog is well known at this stage or not. Once your blog is out there it is out there and there's no going back. Remember the best way to be regarded as an expert is to offer information that is generally found to be correct.
Make your blog readable. The world of the blogger is not an academic one. This isn't the place for you to parade your superior knowledge of adverbs or show how you could star on the BBC word lovers' show, Call My Bluff. It's a world most often read by readers, who are taking a break, sneaking a quick google search when their boss isn't looking, and for a great many looking for entertainment. It's easy to google facts, but to make someone read your blog regularly you're going to have to give them something that is as great a pleasure to read as you can offer.
Tell readers how you know what you do. This comes after readability because you can be the most informed person in the world and still be thoroughly inaccessible. If you're an author like me you quote some of your publications. You drop into your writing how you used to work on international papers. You mention the thirty odd short stories (some of them very odd) you've had published. And of course, you promote your up and coming products, because ultimately the reason you're writing your blog is promotion.
You may be writing to establish yourself as an expert, to help publicize your work, your creations or even your political opinions, but this isn't why people read you until you become very, very famous. Promotion is a side effect of a blog. It's the side effect you might desperately want, but ultimately people turn to blogs for entertainment and information that helps them. Offer your readers useful links when you can. Make it personal in a way that allows them to trust you. For example if you're a writer writing to writers or a mother writing to mothers, emphasize with the very real struggles and challenges these particular occupations land you in. Don't be an all-knowing, all-seeing guru. Offer up the mistakes you've made and share what you learnt. Showing your humanity and a capability to laugh at yourself are endearing traits.
And at this point I should offer a personal story about myself. However, another key issue in establishing credibility, and one that is linked to loyalty too, is not to go on too long. Be assured then that I do poke fun at myself on Write Forward and please drop by any time.