A string weed trimmer should take care of any greenery, but digging down with a knife every year or so can restore it to "new" if you don't keep up with the trimming as faithfully as you need to. If the stepping stones are set in gravel or crushed granite and weeds are a concern, use organic corn gluten to help control the sprouting of weed seed, or let a ground cover take over. Vinegar and hot sunshine can kill a number of weeds. Agricultural molasses appears to be helpful against sedges.
As for tips, place the stones at a comfortable distance for your own walking comfort. Look at different colors of stone samples by day and night. Finding one that gives good contrast to its surroundings by day and night is a great way to make the steps a nice design feature that can be enjoyed at any time of day.