There is no set amount of words that a first blog post should be, as this will largely depend on the topic and audience that the blog is addressing. However, a general rule of thumb is to aim for around 500-800 words. This will give readers enough information to understand the main points of the post, while still leaving room for further discussion or elaboration.
Additionally, it is advised to make sure that all of the key points are clearly articulated and well-written, in order to ensure that readers will be able to follow your argument clearly. Finally, a concluding paragraph or two should provide a summary of the main points made in the post, as well as any key takeaways that readers can apply to their own lives.