First - pick a theme. What do you want to write about. A random variety of topics is ok if you can make that interesting. If you stick to one topic (for example, the beaches of Uruguay) you are much more likely to build a regular readership. Comments and support from regular readers provide a lot of encouragement and momentum to a blog.
photo courtesy of T. Mehta.
Second – be regular. Post several times a week. To some degree quantity matters more than quality. Be prolific and your readers will thank you for it. Spending tons of time editing is wasted time. Everyone loves pictures.
Third – publicize. Mention your blog to anyone you think will be interested. This is how you build a base of readers. Some fraction of people will visit the blog and some will become regular readers.
Fourth – spend some time every month thinking about how to improve your blog. Small improvements make it easier to read and make it look better. It is ok to experiment.
Most important of all, just do it. There is no proper or complicated way of getting started. Write an entry and post it.