There are no specific clinical features that reliably differentiate COVID-19 from other viral illnesses like the flu. Early studies (Study 1 and 2) out of Wuhan show the most common clinical features to be:
Dry cough (~59-68%)
Loss of appetite (~40%)
Body aches (~15-35%)
Shortness of breath (~19-31%)
Productive cough (~27-34%)
Other less common symptoms can include headache (~14%), sore throat (~14%), nausea and vomiting (~5%) and diarrhea (~4%). A decrease in smell or taste has been noted in smaller studies from Italy as well.
Here is an infographic created by Dr. Michal Tal, an immunologist from Stanford on the timeline of frequently occurring symptoms.