I won’t duplicate some of the other advice but I didn’t see this mentioned - when using manufactured wood products, the bonding agents differ widely and some will offgas toxic chemicals when lased It’s important with plywood or MDF to make sure the stock is safe for lasers. Other than always buying Proofgrade plywood and draftboard, I’m not sure if there’s an easy way to certify that.
The other thing I’ll toss into the ring here is an observation on types of wood. When I researched making a cutting board from scratch I read that woods which produce edible fruits and nuts tend to be safe. That includes most of our domestic species like Cherry, Maple, Oak and Walnut. However, some woods, especially those with high oil content or that are very fibrous, can release irritants when cutting with blades or sanding. Lasing is not cutting or sanding but until I know much more about material safety I’m sticking with the same wood species I’d feel comfortable eating off of. These turn out to overlap the Glowforge Proofgrade materials quite a bit - Maple, Walnut, Cherry. I may try Oak but as others have noted it is very open-grained and dense so I would expect getting a nice print on it would require much more experience than I have just now.
“Spalted” wood can be extremely pretty but the spalting is the result of fungus. It is highly prized by woodworkers but usually kiln dried before use. Even so, the fungus can cause irritation if inhaled. I’m not worried too much about the bits struck directly by the laser, but a little concerned about the bits next to the kerf that are ablated into the air.
Last thing in my “wood safety” pitch is that using wood other than Proofgrade leaves you a bit adrift as to settings. Things like moisture content can greatly affect how the wood is worked with metal tools so I assume there’s a similar variability with the laser. Same with knots. High power, high LPI and slow movement might cut in one pass but may also impart enough energy to start a fire. Test on scrap wood. Don’t be afraid to make multiple passes. Just as when working wood with metal tools, patience will reward you.
Good luck! I’m looking forward to seeing some of your work!