Getting maximum out of a Ad campaign

[mrb.frequency]

I have founded a site which sales different coffee related products. I have invested some money in digital marketing ad campaigns so that it may get some exposure and so I can make some conversions. But I have doing it for 3 months and not getting much conversions. Its not that I am not getting CTR's but they are not converting. I have consulted some professionals for my landing page optimization but they had said that it should do fine. So that means I am left with my ad campaigns. If anybody can give some advices then it will be really helpful.