Since doing the PPC experiments I have had a lot of people asking me for help with there campaigns. Just sticking with the ringtone theme I see the same mistake time and time again.
1) People are using International targeting and not limiting to country specific – Hello?!? This seems so obvious but so overlooked.
2) People choose eye catching keywords like mp3, sex, hot chicks, myspace. While these will generate clicks they generally do not convert at all.
3) Adwords – Googles adwords network (ask.com and other spam search results) generally convert horribly. Just stick to Google Search on adwords and venture out from there.