Dwarf French Beans don't need support and should be sown as a single row, about 60cm from other row crops ending up with 8 plants in a row. Start by sowing 16 seeds across the row, 3-5cm deep, and thin later.
Sow in early May so, by the time the seedlings appear about 10 - 14 days later, all danger of frosts should have passed. Sow a few extras in pots in case replacements are needed.
French beans pickings come all at once so it is worth sowing a second row later, perhaps early July, for an early autumn crop.