Yes great topic, good summary by Ramona obviously.
This is a nice introduction to mainsail trim and telltales.
www.rya.org.uk/knowledge-advice/cruising-tips/boat-handling-sail/Pages/trimming-the-mainsail.aspxOther links on that rya site go to genoa/jib trim and telltales but they don't include genoa/jib leech telltales surprisingly - so indicating if the leech is free enough and not too closed hence having the mainsail choking its exhaust. Low ratio fractional rig yachts need to be careful of this - so latest fractional rig yachts have the hounds very high - but older ones have lower hounds as per a % of the mast height, and need to be careful of not choking the slot at the upper regions of the genoa/jib. Leech telltales ate critical to show this.
This link is a good link to genoa/jib telltales as well as the 3 steering trims high, speed made good and low.
www.uksailmakers.com/encyclopedia/53-sailing-to-telltalesOf course North Sails have more on line videos that 100 sticks can be poked at.............