Try the software trial for Geneious it will guide you with primer designing and cloning and later on you can shift to other freewares available online and offline.
Make sure your primers are specific to your gene of interest and do not amplify other targets in the genome.
If you want to get the entire coding region, make certain that your primers surround the entire region and a bit extra.
Depending on your cloning technique of choice, you may need to incorporate restriction enzyme cut sites into your primers. Use software to help you so you don't get them in the wrong orientation.