For new websites it may take some time,so be patient. Google will rate according to your updating frequency, backlinks etc. For older websites, if you are facing indexing problem, make sure you do not have internal or external duplication of contents. And do not rely on sitemaps. Because they are optional. Make sure the contents can be searched via normal links.
There are many reasons tha could make your site "slowly indexed". But here are some tips that can help you to improve your search index:
- ping the search engines'
- submit your website to social bookmarking websites;
- submit an XML sitemap to Google;p
- use fetch as Google bot tool.