at the scene settings for the shutter speed. Than after shot in TV mode and adjust the shutter speed either one or two stop down.
It involve practise seriously, you can train by shooting pets like cats in your area.
TS - if you are still having problems, it may be better to get someone knowledgable to show you how flash is able to assist. That is probably the easiest way.
100D is a great camera. Don't be tempted to "upgrade" to 70D because it won't solve your problem unless you are talking about Full frame like 6d or 5dmk3 where Iso at 12800 is better than your crop body iso at 1600.
Yes, get a small & light flash like the 270ex2, flash head face up with diffuser, always set to HSS, set flash sync speed to auto in AV mode, in AV mode, control your resulting shutter speed using ISO.
| 5Diii | 24 ii | 40 | 24-70 ii | 24-105 | 70-200 F4 IS | 270 ii | 600EX-RT |