What is the best way to lay flagstones to make a safe walkway?

did you first lay down a base of sand for the flagstone to rest in/be levelled with? There is a product available called polymeric sand that you can use as a base...the benefit is that once your pavers are placed and you put more between the cracks, it gets watered and gardens like a cement keeping the pavers in place and weeds out

Bedding them on Sand and Cement

When we put down one walkway, we used decomposed granite as a base, then sort of jiggled the pavers down into the DG a little ways until it did not rock or move. Then we we dumped more DG over the top and swept off the excess with a push broom, and used a light misting of water to settle the DG. This left the paver flush with the surrounding surface.