For the best start on next year's garden, pull the weeds this fall. If you can get your hands on any compost, add loads and loads of it to your soil and till it all in. I struggle with clay soil, too. Leaves are free and plentiful in the fall, so I add copious amounts of shredded leaves each fall and just turn the soil over the leaves with a flat-tined pitch fork. The compost and/or shredded leaves will improve the soil and turning the soil over in the fall can expose and kill weed seeds.