You need to post content regularly. Whenever your post new content google crawls and give position to your blog.

One thing you can do to increase your crawl rate is to go into Webmaster tools>your site>Configuration>Settings>In Crawl Rate>Let Google optimize for my site (recommended), if it is not checked.

If it is already checked then another method is to fetch as google for that go into Health > Fetch as Google> and click fetch you homepage and then click on submit to index.

This will increase the crawl rate of your website.

Hi
Google gives priority for website which updates its content on regular basis . And check whether your server support if modified since HTTP Header this will indicate the boot that the website has something new to crawl.

Google takes time to crawl the websites which are.As you have said your site has been crawled one time in a month then it may be possible that Google will come back to your site once you will update it and provide unique content on it.Updating the site frequently will also prove fruitful.And the best part is to check whether your site is submitted on webmasters or not.If not then submit it and see the results.

In case of keywords may be you are not optimizing them well,means you are not building quality backlinks can be the reason.

For crawling of new site or page you need to do bookmarking for that page. Or you can ping by pingler, pingomatic etc.