A quick way of moving this process along is to type into the Google search box the first few letters of your topic and see what words appear below. Write these words down, then add a couple more letters again write down what appears, complete adding letters to the word and repeat the process with the words that appeared. This will give you keywords from which you can build up the text for your ads. Then add these topic keywords into Google adwords search which will give an indication of interest and competition for the sector you are researching. With this information you can build lists of relevant words into phrases or sentences to use in advertising campaigns.