This is the ideal way of creating a wildflower meadow. Good ground preparation is essential for success. The secret is a low fertility soil. A fertile soil will just cause vigorous growth of a few grasses and 'weeds'. You can reduce fertility by stripping off the top 5-10cm or so of topsoil. Then lightly rake and roll the soil to produce a seed bed.
The best time to sow your wildflower seed is in early autumn. You can sow in April, but many seeds need the cold winter months to break their in-built dormancy. They will therefore not germinate in their first year from a spring sowing.