1) Move wire to another same-size circuit breaker to eliminate bad circuit breaker as suspect.
Do NOT increase size of breaker or it will cause fire.http://waterheatertimer.org/How-to-replace-circuit-breaker.htmlhttp://waterheatertimer.org/Troubleshoot-household-electricity.html
2) Put hand on each appliance and outlet to see which ones are warm. Outlet should never be warm or hot. Replace outlet. Inspect wires for loose and burned connections.
3) If the breaker is good, then add up total watts being used by checking watt rating on each device. 100 watt light bulb is 100 watts. Big screen TV has a label that shows 300 to 500 watts. Computer has label. Space heater has label showing 1500 watts. Iron has a watt rating label. Take total watts and divide by 110Volts and this will give amp load. Total watts used = 2000 and then divide 2000 by 110 volts = 18.8 amps
Compare amp load with circuit breaker.
20 amp circuit breaker has 80% safe maximum, or 16 amps.
If amp load is 18.8 amps, then 20 amp breaker is starting to get hot, and weak breaker will start tripping.
If amp load is 18.8 amps, and breaker is 15 amps, then you are overloaded and breaker is feeling the heat, and tripping because of heat.
Solution is to reduce amp load.
4) If you have short circuit, that can also trip breaker.
Unplug everything and then plug things back in slowly to see which plug or appliance is causing the problem.