Lazy horses, hard-sided horses, and stubborn horses are all horses who have gradually been desensitized to pressure. What you need to do is 're-sensitize'. The way you do that is by using gradual increases of pressure, starting out with your ideal. By receptive to your legs, do you mean when asking for forward motion, or lateral (sideways) motion?
Firstly, you need to decide on your goal. It may be your horse loping off a kiss, moving off in response to a tightening of the calf muscle, a bump from the heel… Depends on your discipline and personal preference. Then you need to commit to ALWAYS beginning with your ideal. There is no way you will get the response you want to begin with, but that is the point. You need to first, ask using your ideal amount of pressure. When that is ignored, you need to increase it. If it is ignored again, you increase again. I always only use three steps. I was always taught it through the saying “First you whisper, then you speak, then you shout” or “Ask, tell demand”. The way I do it? I start with my ideal, then move up to a stronger aid, and if still no response, I make that horse think that the sky is falling in. Yelling, waving arms, over-under with my reins, huge push with the seat and strong leg aids. They will go, and they will go now. I then let them travel at that speed without interfering, except to keep them going if they try to drop back. The most important thing is that once they have moved off, to sit quietly and let them just move. Getting angry serves no purpose. Once they have maintained it, drop back and start again.
Eventually, they gather that if they move off your first cue, they avoid the falling sky. Works like a treat.
I also find that if it is a forward issue (i.e. lazy) then the trails are the best place to work on it.
Spurs should not be used for forward aids. They refine already solid aids and allow for subtlety in applying forward and lateral aids. I show my ASH in spurs and occasionally train in them, but 80% of my riding is done without.