Sorry to hear that.
There is no specific waiting period for reapplying. You can either apply online or through an agent (a good one). Ultimately you have to do due diligence to make sure you are providing all valid documents/information as required in the checklists. For fund of host, my wife provided 6 months bank statement in Canada, pay slip of 6 months, notice of tax assessment (if available, should be if you lived here in 2016), commitment to support visitor in the invitation letter. Review the country specific checklist while collecting documents. We also provided the visitors bank statements (6 months), source of income etc from visitors country.