How can I best develop off-season?

This is your best growing time for your area if your in Vietnam. The rainy season is ending and cooler temperatures are coming. Best thing is to grow indoors for a few weeks until your plant has a good root system then put her outside in half day sun (Morning /early afternoon sun then late afternoon shade) for one week to get her used to the sun. Then put her into full sun.

By starting your seedlings indoors. So when it's time to go outdoors it can be a month old and a foot tall for example. U can also build a green house and get a 100 percent light proof black tarp to throw over it. Then u can induce flowering when u want to. So u can get 3 harvest a year outside. Or just get a grow tent doesn't have to be big to put inside and grow throw winter

By growing indoor and controlling the growing environment

What do you mean by develop off-season? Like outdoor grow during winter? If you live somewhere that temps don't get too cold in the winter then you could build a greenhouse for the plants to help protect them and give you a place to hang lighting to extend the hours of light the plants are getting so they don't flower immediately. If you live in an area where winters get pretty cold then you would have to figure out a way to heat the greenhouse as well. Other than that the only other thing you could really do in the offseason would be to grow inside.

Careful by not giving too much water. Make sure soil drain well. Use extra amount of mix to help drain. ie pearlite, coconut husk, pucmice. Make sure not too much nitrogen. Not too much phosphate. Be extra careful with manure, bat guano, bone meal. Use worm casting. Give humic acid to help plant eat food in low light. Use trichoderma and chitosan to prevent disease. Peace and stress free growing.