I am not an expert at all! But I have done 2 clover plots. One I sprayed really good twice with gly to kill everything and it looks very good. The other I sprayed once, and then broke the ground up and it has a lot of weeds. My suggestion sounds like it will be late for you, but the biggest thing I would say is kill everything first. I spray, let it die, disk it up and give it time for any buried dormant seed to germinate then spray again. This worked very well on my "good plot", and I am spraying my 3rd plot tomorrow so I am ready for late Aug planting.
Also even on my good plot, I planted it in the fall and it took until the next spring to really do much.