On my own two single speed bikes I have always just pulled back moderately hard on the wheel with a hand on each axle nut. THen I finger tighten the nuts while pulling. This produces the correct sort of non tension but not loose chain that works nicely. If your bike has screw tensioners then at that point just bring the screws up to contact without adding any tension. The real role of the tensioners is as an axle positioning device and they should not be used to jam tension into the system.