If you have a greenhouse or lean to and you can shelter plants under glass until warm weather arrives.
A good tip is to plant up a hanging basket or tub and grow it on in the greenhouse. This gives the plants time to settle and establish roots in the container, in the snug warm of a greenhouse. Bedding plants grown under glass will need to be "hardened" off before planting out. This means getting the plant accustomed to the outside conditions and not moving it straight out from the calm, still and warm greenhouse ( yours or at the garden centre,) conditions to the less perfect outside weather. Move the trays of bedding plants outside, starting on milder days and leaving out for longer as the weather improves until they are out all the time and fully accustomed to our weather.
Bedding plants are attractive to slugs, some more than others. For example, Marigolds are slug magnets, but Calendula are not. Protect with slug protection, such as pellets or slug traps. Check out Best Bedding plants for ideas on which bedding plants are slug resistant and which are low maintenance.
Bedding plants have to grow and produce lots of flowers quickly, in just a matter of months. It follows they will do best in good compost and will always benefit from feeding during the growing season.
Dead heading is essential to keep bedding plants flowering. In summer, when in full bloom, dead heading may need to be done several times a week depending on the plant. Some bedding plants are easier to grow than others. For example, Mesembryanthemum common name ice plant is a fabulous showy bedding plant, bottom left, but look at the dead heads in the image next to it removed in just one day. If a plant is not dead headed, it will cease to flower, but taking off 50+ spent flowers is time consuming. Compare that with a Pelargonium, (image 3 top right) which needs much less dead heading and Nasturtiums, 1st image top left, hardly need any attention.