A good way to evaluate conversion paths is to understand how long it takes people to convert and how channels interact along the way.
Use #Google analytics Top Conversion Paths report to look at sequences of unique channel interactions (paths) that led to conversions. You will find this report in Multi-Channel Funnels section of Google Analytics. the report shows the number and value of conversions for each sequence. Chances are, the paths will be very diverse: 3%-5% of visitors followed the top path. But there are still trends you can obtain from this report.
Skim over about 100 top conversion paths. If Referral is a stranger to the party, examine traffic from referral sites and find #links that bring you good converting traffic. Then, try to get links from more sites like that because you need to work on your links.
If organic traffic starts most of the paths and paid terminates them, you need to up your #SEO game. Your visitors find you in search but until they come across your ad, they are not convinced that you and them are a good match. If PPC starts the conversation and search brings home the bacon, you could be wasting money on PPC and a paid search audit might be in order.
All of the above are a starting point of an investigation. You will have to dig deeper to prove or disprove the hypothesis.