Ground Clearance
Wildflower meadows are not fussed about soil quality, so theres no need to feed or fertilise, however they are botherd about weeds and grasses which can soon take over a meadow if not cleared before sowing. It's important to get back to bare soil or as near as you possibly can.

Planters pots and window boxes
When preparing your pots, planters and the like ensure that your soil drains freely.  Make sure your containers have drainage holes. Placing pieces of broken crockery or stones in the bottom of containers helps to allow excess water to escape. With regard to soil, standard run of the mill compost or sterile topsoil is perfect for the job. Water your container ahead of sowing. If there is any sign of waterlogging you should adjust the drainage to stop this

Existing beds and borders
If you are going to sow into existing beds or borders ensure that all old growth is removed. Weeds such as danelions and docks have a deep root system (known as tap roots) and you should try your best to remove these to stop regrowth. Any woody root systems, such as those on brambles and the like, should be removed. Try not to disturb the soil too much during preparation as this can expose and activate weed seeds that have been dormant in your soil. Lightly rake the area and remove any stones.

Grassed areas
If you are converting lawns or grassed areas they will need to be cleared. Our field trials found that two methods of clearance stood out as the best for our blends. 
The first method is to remove the top layer of grass and any weeds to a depth of at least 2 inches (5cm), and then gently rake the bare soil, removing loose stones as you go.
The second way, which is a lot quicker and less physical, is using the no dig method of ground preparation. This involves smothering the grass (and any weeds) to shut out daylight, and as a result the grass and weeds die away.  
For those interested in using the no dig method we have put together a seperate guide.