I normally use a sliding bevel and a square off the tile below for these cuts. Quicker than a template and if you have more than 1 cut at the same angle you just need to measure the size of the smallest gap between tile and wall/ceiling and offer use the gauge
Exactly what beanz said also if the angle is the same use a bevel other than the grout lines you always have a few mm tolerance, you can always have upto 4mm Silicon lines round edges, double masking tape or fugi kit is good I've progressed to home made sticks now, still marvel at the pro masticers