Ok, $300 is a good amount.
First, size. Dreadnaught is the typical guitar size. It’s big. Most of the guitars I’ve owned have been dreads. I still own 2 or 3. Only real problem with it is that it is a little uncomfortable to play for a long time if you’re sitting down, for some people anyways.
000, which is “triple aught”, auditorium, concert, “OM”, and folk are all similarly sized small body guitars. I recommend these sizes or a Dread for your first guitar.
Other sizes aee Jumbo, which has a bigger boot than a dread but is otherwise similarly sized, 00, which is smaller than a 000, 0, smaller still and also known as a parlor guitar. I wouldn’t get any of these for your first. The single exception to this would be the Taylor GS Mini. But I wouldn’t get a Taylor - they make excellent guitars, but to me they all sound tinny and soulless. But this is a Chevy vs Ford argument.
Look for a SOLID spruce top. Preferable back and sides too, but don’t be too picky. The top will at least get you into something that sounds decent. X bracing rather than ladder bracing, unless you want a cheap blues sound (cheap meant as a discriptor, not a knock... it’s just different). I also would want an adjustable truss rod.
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Preferably solid Back and sides, but laminate is fine. I would make sure they have a real name for the back wood though. Ideally, even if it is laminate, it will be Mahogany (or Sapaele), Rosewood, Maple, or Walnut. If it says “Natural back and sides” or naturo or nato, or nothing, or if it is painted black, and it is not a black guitar, avoid it.
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Yamaha will be good if you make sure it has the solid top. And some of them are really, REALLY good.
Epiphone is ranges from E36 M3 to superb; their Masterbilt line is good to phenomenal - this may be where I’d look the hardest on the used market.
Ive never really been impressed with fender acoustics and would stay away. Others have had better luck.
Ive bought a Larivee for $300 that is superb, probably won’t find one but if you do, keep that in mind.
Seagull will probably be in that price range, maybe with a cedar top (which is fine, I just prefer spruce), they’re good guitars but I’ve never fell in love with them myself.
Washburns are generally pretty good for the money. Not great, but not bad.
Cort, Samick, Peerless, among some others are OEM manufacturers that range the whole gamut of imported guitars. I’d avoid these until you know what you’re looking for or have someone going with you.
Martin, Gibson, and Taylor are the big boys. Probably out of your price range except for the Little Martin (meh), Baby Taylor (meh) and Taylor GS Mini (not bad).
Also buy a Keyser Capo, a tuner, and budget $50 to $100 to get it set up. Ask around for who should set it up. Tell them you like low action and use light strings until you build up calluses.