Ive started a blog recently but am still fairly new to the idea, should you just write a seperate article for each product and service, or do you write it on news in the industry (or both)?
If i were you and I was going to promote a product by blogging, I would write one blog for one service or product. If you are going to market something with your blog, I am going to tell you the realization that it takes time. Your blog should have a lot of content, before you are going to start to get any results. I'd say that you need anywhere from 30-100 blog posts, to make something happen. Good luck with your endavours!
The best is to write a variety of blog posts to attract different readers. However, blogging to promote products is not easy. I suggest you do article marketing instead.
Promote your product or service with different creative articles. Make them funny/interesting/informative.
Do write some good posts then think abt advertising. If there are no content, how the visitors will come ?
This will depend on your blog niche. If you have a personal blog than you can make a post whatever you feel good and happy to share it on your blog, it can be opinion, news, story, review, or you can also look other people blog to find some ide (same with your niche) and google trends, and many other things, so understand what your blog target first before you make any article inside it. Just for example : If you have a weight loss blog than dont write article about making money in your weight loss blog.