One route I take home has a couple miles of flats and then a 5 mile long uphill (Capital Cresent Trail rail trail). I usually let another rider or riders pull on the flat section and pull for a few minutes on the uphill section before attacking. Helps make the uphill grind a little more interesting and overall speed higher than riding alone. Sometimes the train stays together, sometimes I'm dropped, and sometimes I "win." Pretty safe given the lower speeds involved.