Auto Renewal here.
I send out a cover letter with greetings, thank you's, updates, and reminders of cool extra services like the insect controls, aeration, seeding and tree/shrub care. I also remind them of referral deals that are in place or any other teasers.
I include a printed copy of their scheduled services for this upcoming season, which is always the same as last season unless discussed prior.
I include the pre payment deal (5%) and include an envelope.
I suck at raising prices. Honestly? I don't hardly ever do it. Fortunately for me I charge plenty upfront and am not low bidding too many jobs.
I do however stick to a pretty tight pricing structure that goes up with the times, or down as my market prices adjust.
I never mail anything out till mid February. I am in Michigan.