Sam, the advice I got on here, which helped me, was to sort out saddle height and reach:-
Saddle height - when sat on the saddle, with a pedal in the 6o'clock, position, your heel should just touch that pedal, without having to reach. This got me a saddle a lot higher than I expected, I can't touch ground either side. It isn't perfect but will give a close approximation. To tweak further I used the idea, pain/ache in front of knee, saddle too low, in back of knee, saddle too high.
Reach - this was harder for me to work out, you need to get your saddle in the correct position on the rails. Then you can tweak bars via length of stem, spacers on steerer tube and angle of stem. I found this trial and error and needed Aperitif on a ride to actually sort rails bit with me. The rest I've just kept tweaking til it felt good.
Point to note, measure/mark all positions before adjusting, so that you can get things back and also know how much you've moved stuff.