There are a couple of very common mistakes made by DIYs (and some contractors).
Mistake number 1 is cutting out your bed before picking your plantings. The tendency is to cut a 3-4’ wide bed and to plant 1 ½’ from the wall of the house. Very few plants will have enough space in this scenario. You will soon regret or remove them.
Another goof is to not ask for help at the nursery. It is human nature to start your search by asking for the things you know such as lilacs and rhododendrons. They have nice flowers but will very quickly outgrow the spot. Make the bed size appropriate for the plants you choose.