Bentley you can work out your soil type by picking up a handful of wet soil and squeezing. If it sticks together it's clay, if its really crumbly it's sand and if its in the middle it's loam whcih is the ideal for many plants. When it's dry, clay is rock hard.
Roses and clematis like a rich soil, which clay and loams tend to be, as the goodness stays put: it washes out of sand. I give my roses and clematis a dose of rose feed in February and June, and spread rotted manure round the base after the February feed ('mulching') to give them more food, keep them moist and to improve the soil. Soil improvement is key to successful gardening for many things. Manure and garden compost (compost that you make yourself, not the bags from garden centres) really changes things: if you have clay or sand adding these makes the soil go more towards loam. I use well rotted manure from a local stable and also bags from garden centres.
Some things though as noted by Maud like poor soil eg lavender, rosemary.
You could try planting annuals from the garden centre like lobelia (small, blue or white, pretty) or cosmos (ferny foliage, pretty flowers, pinks).
If you plant a perennial geranium (which is a good idea) I wouldn't choose Johnsons Blue: it's lovely but doesn't flower for long. I'd go for Orion or Brookside for blue, Russell Pritchard for deep pink and Mavis Simpson for pale pink. The specific Varieties of plants can make a difference: if a plant is marked 'AGM' that means it's a good variety: it has been tested and has an Award of Garden Merit from the Royal Horticultural Society.
I buy small plants like perennial geraniums which are cheaper, and they grow quickly once planted, not the mega pots that cost £8.00 or so.