How can I increase my hit ratio in Memcache?
I would interpret the numbers in a way that 70% of the traffic to your site are pages that are currently contained in the cache. The other 30% did go stale because the weren't visited frequently enough to stay fresh.

This is a more common problem about "How to cache?". The base Drupal cache is time based. If you don't use more complex methods like Drupal 8 tries to do for you there will always the problem that from time to time hits can't be cached. So probably 99% of you home page are cache hits. The 1% are the hits while the page is refresh. But any other page that is older than your settings on the "performance" settings page will be immediately stale. Means that if you cache for 5 minutes and the page is visited every 6 minutes it will never get a cache hit.

Your cache is currently more or less a protection against traffic spikes or (D)DOS attacks. But not something that really eases the web server in all occasions.

Real solutions for this go above this question and the easiest thing would be to go to Drupal 8. It really tries hard to cache your stuff for ever.
http://buytaert.net/making-drupal-8-fly

All in all 70% is not that bad. You could try a module like boost:
https://www.drupal.org/project/boost

And than find a way how to cache things until they are updated. But if you use a sidebar with views this will be a big problem if you don't go using asynchronous (AJAX / AHAH) calls by javascript or things like edge side includes (ESI)