Before you start your own blog, you must keep in mind the golden rule to fetch organic traffic - quality content plus appropriate SEO are the king features to rank a blog high in the Google results. And remember don't start a blog on multi niche as it will be very difficult to cope with the updates of all the categories. Start a single niche blog like as you already mentioned to run a technology related blog, the best way will be to built a comparison blog. With your tech-comparison blog you can compare smartphones, tab or related hardware. In doing so provide a detailed description with adequate images in it.
Now let's focus on the white hat SEO. Whenever you write a blog post, keep in mind the keywords which you are going to use. For example, if I want to compare Panasonic Eluga S and Lenovo S580, then my title would go something like Panasonic Eluga S Vs Lenovo S580: Detailed Comparison. Now after a perfect title, summary or meta description is the next part we ought to optimize. Now, the first sentence of summary should have the same keywords which your title has. For example, summary should go like - Check out the comparison between Panasonic Eluga S Vs Lenovo S580 (Note that I used Vs instead of and). For a perfect summary, You should always try to truncate your summary to not more than 160 characters. Now, after providing a summary, we have to SEO optimize our article's content. When you have written the whole content (without taking in mind the SEO optimizations), write an introductory paragraph comprising of your keywords. But remember do not do keyword stuffing as it will have negative effects on your blog. For this purpose, you can keep a watch on the competitor's website on how they use keywords in their content. After completing your content, check for the keyword density (use online checkers). For a safe SEO, your keyword density should be between 2-4% and never more than that. Now you have successfully optimized your content for white hat SEO.
PS: Although it is optional to optimize URL for the keywords you used in your content, but it will not be a bad choice at all if you well optimize it with "-" operator separating all the individual keywords like "panasonic-elugas-lenovo-s580". Never use underscores in your blog URL.