Hi Chris. I'd start by having a look in books and magazines - or online - to get an idea of the 'look' you'd like - contemporary, rustic, formal etc. and decide whether you'd like some scented plants or more of a foliage look. Some evergreens are probably a good idea as they will give structure all year round and you can add colours and flowers through the seasons with bulbs in late winter and spring, and some summer flowering annuals or perennials, or use shrubs which flower at different times.Do you have colours you particularly like - that's a good starting point.
No matter what size your patio is try and avoid lots of little pots here and there. Grouping larger pots together is always a better look. If you have a long run of wall you can do a line of pots all the same and with the same plant/shrub which is very effective. A set of steps can have matching pots each side or a run up one side of the same thing. If you don't have a lot of time you'll need impact but not maintenance. How you use the plants is the key. Once you decide on the look it's easier to make actual suggestions on the individual plants.
If you can put some pix on that will help too. Hope that's of some use