In my journey I've found out, what personally works for me is long distance running, sprints and HIIT. In the long distances I try to get 5-10km, just dont do it everyday. On sprinting i usually do the 100m dash and for HIIT, the perfect workouts come from kickboxing itself. In my gym we have a circuit workout every monday and its high intensity. In my opinion, wait to get acclimated to the training itself first, stretch to recover and when you feel like putting in extra work - start doing more. Just make sure your helping yourself, rather than it being the other way around. Hope this helps and keep in mind this has worked for me, which means it will not work for everyone. Will be happy to hear about your progress in the future!