Be aware that weed control is a game in which you can stay ahead, but never "win." Weeds are just too persistent ever to give up. While landscape fabric is supposed to prevent buried weed seeds from ever becoming full-blown weeds, landscape fabric does not, in fact, stop some of the tougher perennial weeds (or grass) from pushing up. If you know you are battling plant pests that grow from rhizomes or stolons, eradicate the rhizomes or stolons first. Then lay landscape fabric, upon confirmation of eradication. In overgrown areas, killing weeds is only one part of an arduous process of "landscaping from scratch."
Landscape fabric can be laid after a bed has been planted. If plants were already in place in my planting bed, I would cut slits in my landscape fabric where needed (working from the edge to the middle) as I unroll it over the bed and neatly tuck the flaps around the plants' trunks. Instead, I'll be making x-shaped incisions in the fabric where I wish to install the plants (Step #8). The incisions will be just big enough for digging a hole for the root balls of the plants. The fewer and smaller the holes you put in the fabric, the better.
Landscape fabric should be installed over ground that has been smoothed out. If laid over twigs, stones or existing weeds, it could be punctured. I recommend 2 tools for smoothing out the ground: a hoe and a steel rake.
As we'll see on Page 3, the hoe is used to eliminate standing weeds....