To bring it down to a very basic level, assuming a low CTR is your concern:
In my opinion a very low CTR means that for one reason or another, people searching on Google are not finding your ads relevant to what they searched for, and/or there is simply something about your ads which causes users to decide against buying from your business.
In the first case, a likely solution would be to use keywords which are very targeted to what you have to offer (as opposed to being remotely related, or worse, unrelated) - and then have these keywords bring up an ad that is about exactly same thing as the keyword. By doing this you create a situation in which, when a user searches for something, they see your ad about the exact same thing they just searched for.
In the second case, the issues could be many. Some of the more common issues might be:
* The ad is not about the same thing as what they just searched for (as outlined above)
* The ad does not catch the attention of users for some reason, and it is ignored
* The ad is badly written, and while it is not ignored, it does not reflect well on the business that created the ad and actually makes a negative impression
* The ad has grammatical errors or errors in the arrangement of the words, which do not reflect well on the professionalism of the business that created the ad
* The ad copy does not describe the product or service in a compelling way, or does not offer a reason why it should be purchased from your business in particular
* and so on...