Hi Flyfish - That's a good start, the key is to practice having done so myself over the years.
I got into bridle sewing in order to address a problem I was having with a couple of my open cell foils. I replaced some bridles on one kite and made a set of "A" Primary's & Secondary's for the other kite. I also received some excellent advice from someone that worked for a pargliding/kite company at the time.
A few tips that have helped me:
Select the correct size needle in relation to the sewing thread being used.
A needle too big will produce a poor quality stitch.
A needle too small causes the sewing thread to catch as in penetrates the fabric resulting in a poor quality stitch
Ensure the upper and lower thread tension is 100% correct to ensure the crossover between the upper and lower sewing thread takes place in the middle of the fabric.
Use quality sail makers sewing thread. (Polyester thread)
Designate a sewing machine for a particular sewing task this prevents the need to have to keep re configuring the sewing machine.
Check the setting of the sewing machine regularly monitoring the stitch quality as you sew.
Don't sew when you are tired and always work in good light.
When starting you could put a fine needle through both lines to keep them together, or wrap a strip of spinnaker repair tape which works very well.
I also have a sewing machine with a lower gear function, this allows me to sew very slowly.
The attached is an example of what can be achieved with practice