Posted: 02/09/2017 at 20:07
It's a big subject and also depends on what sort of soil you have, acid or alkali, heavy or light and whether you will be planting in sun or shade. Some plants like it most and others are happier dry.
I started years ago by buying a book about perennials, then walking up the street to see what others had planted that I liked and looking them up in the book. Nowadays there is the Internet which is a huge source of information and garden centres have lots of well labelled plants.
Another thing is your own personal taste. Do you prefer spikes like salvias or daisies like rudbeckias? What colours?
I would start with the easier plants, like hardy geraniums, salvia nemorosa, rudbeckias, phlox, tiarella, campanulas, aster Monch, day lilies. Also plant bulbs, daffodils, tulips (after November), snowdrops, crocus, allium Purple Sensation.
It takes time and practice to get to know plants and your garden. Some will grow well for you and some won't. Good luck.