Hi! Welcome to Daysailer World! Answering your questions, I definitely agree with GreenLake up above, but you did ask a very open-ended question. What do you need to know? Depends on how much sailing experience you already have. I'll chime in here under the assumption that you're not totally new to sailing, but transitioning from another boat. With that in mind, some things to know:
-The Daysailer acts more like a big dinghy, not a small keelboat. Mostly because it doesn't have a weighted keel! This means that where you place your own weight is very important (trim). For instance, if you sit too far back, you dig the stern in and go slow (upwind anyway, downwind is different). Sit too far forward and you'll affect your steering. Generally, sit in the middle, meaning get a tiller extender. Likewise, be prepared to hike. How hard? Depends how fast you wanna go
-You should sail the boat flat, 15 degrees heel at most. This for speed, not danger of capsizing - despite no keel, the DS has a lot of initial stability and is hard to capsize. You can get her up on her ear with no problem, green water coming over the coaming and into the cockpit. However, any further than 60 degrees or so and you're going over! Don't capsize her, this is a very hard boat to self-recover.
-Don't cleat your mainsheet, hold it in hand. Jib too, especially if wind kicking up. The DS is not as "twitchy" as - let's say - a Laser. But you still want to react fast to any changes, and cleating the sheets down is just asking for trouble. But by "fast" I mean seconds, as opposed to Hobie-Cat or Laser fractions of a second. Between holding the sheets and the tiller, you still have time to sip your beer
And having a crew along definitely helps - the DS can be solo'ed quite well but 2-person sailing is definitely better.
-Downwind, this boat will plane, quite easily for a 17-footer. Sit back (move your weight aft) and enjoy the ride!
-Get a good vang setup as soon as possible. Not an absolute "must" have, but certainly the #1 "nice to have." Search on this forum for details.
Speaking of search, the search function on this forum is less than ideal. Use google instead, search: site:https://forum.daysailer.com +"Your Search Term".
Fair winds!
Tom