Clover / Chicory mix is good advice. Better advice is to get out the chainsaw and open up the sky. Cut in a southern and maybe a lil east (preferrably) to get more direct sun. I like going SE vs. SW cuz the dew is still on the plot and the afternoon sun is hotter. Or straight south.
I can't tell ya how many times lack of sunlight has hurt me. More than lack of rain or bad soil. Mainly because I'm have to make my plots out in a mature woods. Lots of chainsaw time and seat time in a bobcat popping out stumps. I'm about 10 years doing plots and learned alot the hard way. 90% of way I do is simple clover chicory (a killer annual that you don't mess with for 4-6 years after its going) and a lil oats or wheat in fall.
So in summer, when the leaves are on, if you look up and cant see a blue area at least as big as the plot you planted.... time to make a lil firewood. I try to open the sky as big as the plot , plus the I cut to the south as far as the trees are tall.