Congratulations on your wonderful new scope! You are doing great having already seen the Moon, Jupiter, and Saturn. I still remember my first time I saw Saturn, truly breathtaking.
The 25mm EP and barlow are great to start with. You are correct about Saturn "coming in and out of focus", that is what you call atmospheric seeing. The lower your target is in the sky, the more atmosphere (air) your scope most go through to reach your target. That coupled with any turbulence will cause views of objects to shimmer. Your best seeing is straight up overhead, at the zenith we astronomers call it, as there is least amount of air to look through and views are best here. I am guessing you were viewing sometime early last night and Saturn would have been fairly low yet.
There are already some good recommendations here for you but I will leave some as well for you to consider.
1. Moon Map - Sky and Telescope's map of the Moon. You can get this for $13 plus shipping off Sky and Telescope's website, shopatsky.com. The full Moon is, in my opinion, the least interesting Moon phase to observe. My favorite is 1st Quarter waxing. I absolutely love cruising the Terminator (interface between shadow and light on the Moon) because it is at the Terminator where you will truly see spectacular detail and depth in craters, lunar mountains, etc. Check out astroleague.org. This is the Astronomical League. They have observing programs for ALL skill levels, beginner to expert. I have been working their Lunar 1 program and it is a blast. Check it out.
2. Bright objects visible with your naked eye you will be able to find with your EZ Finder. Once you start hunting deep sky objects (galaxies, star clusters, globular clusters, nebulae, etc) you will need to locate these objects by starting at a bright star visible with your eyes first and align the telescope with the star. Once aligned to the star, objects are found by "hopping" from star to start, and eventually the object. Light pollution makes this more challenging by washing out fainter stars and making them invisible to your eyes. Your 25 mm eyepiece is actually a pretty good "finder" eyepiece. It should give you a field of view of about 1.0 degree of sky in diameter, twice the size of the full Moon roughly. You can use this eyepiece to START finding objects, but here are a couple of recommendations -
- You need a sky atlas. I wholeheartedly recommend Sky and Telescope's Pocket Sky Atlas. I have had mine for about seven years now and it is holding up very well and even as I hunt fainter and fainter deep sky objects, I still love to use this atlas because it is so handy! For $20, this atlas is a steal and will last you a lifetime. The atlas has a scale that shows you how big 1 degree is. I went to Hobby Lobby and bought some cheap metal hobby wire and string and made a couple of finders that I have tied off to the binding of my atlas. These metal rings show roughly what I can see in the sky with my telescope's 8 x 40 right angle finder as well as my low power "finder" eyepiece. I still use these rings as I hop from object to object. I will post a photo for you to see.
- Invest in a correct image right angle finder. Orion makes a good 9 x 50 finder, I personally use a 8 x 40 by GSO. It doesn't go quite as deep as a 9 x 50 finder (lower magnification and smaller lens) but works fine for me. You will also need to get a second dovetail base. You can drill a small hole in the tube adjacent to your EZ finder to mount the new dovetail and finder (be sure to keep the scope flat or pointed down so the metal shavings don't fall on your mirrors!). I have a Telrad, which is similar to an EZ finder, and use this for "coarse adjustment" to initially locate a bright star. Once I am centered on a bright star, the 8 x 40 finder takes over and I hop from there to whatever object I am looking for.
3. Get a cheap red flashlight. Walmart often has in large bins 99 cent pocket flashlights that are LED. I buy these and use some of my girlfriend's red nail polish to paint the lens red with a few coats. The light should be dim. Even if it's red (red light least impact to your night vision) it can still be too bright and hurt your night vision. There are nicer lights out there for more money. I like these because they are simple and cheap and take AA batteries. I keep a spare battery or two and light with me at all times. The light is on a long necklace and I keep it around my neck all night so I always have it for looking at my atlases.
4. You have a Newtonian Reflector. Newtonian's require their mirrors to be periodically aligned (collimation). Your scope has a focal ratio of f/8 which means the focal point (where your image appears and can be focused on) is eight mirror diameters down the tube from your primary mirror. For a 6" primary mirror (203 mm) that is 1,219 mm. f/8 is considered fairly slow in terms of optics and your mirrors do not require as precise collimation as a scope that say f/4 does. This is not a bad thing for a beginner. Even still, your scope will perform best if you learn to collimate your mirrors. There are many good articles on the reflector forum of this site that can help you. This can be easy to over-complicate, I wouldn't touch the secondary mirror for now. It is probably fine from the factory unless the previous owner tinkered with it. A simple sight tube/cheshire combo tool is inexpensive and will give you very good results. Plenty of manufacturers make them and you can get one for about $20. With your telescope being a solid tube, your collimation will only need to be adjusted rarely but should be checked often especially when you start traveling with your scope and it bumps around in your car.
5. For a spectacular intro to deep sky objects, begin with the Messier list. There is an observing program on the Astronomical League for this and is by far the most popular observing program. The objects in the list are SPECTACULAR. You will love it!
That's all for now...Now I wish my clouds and rain would go away.
Take care and enjoy,