There are many ways to optimize the conversion rate. Although you would need to analyze the current response first. You should see some signals which gives a hint towards the problems. For example if your CTR is very low, probably the communication is poor.
You can try variations with different visual appeal and communication statements. Similarly its strongly recommended that you plan your audience segment very well and create different campaigns for every segment. Similarly for every segment, plan different visuals and communication.
You should also try variation of landing page and see the responses.