I live in the space coast area of Florida. I too have found some driftwood and I was able to safely use some of it, no problems.... Being able to identify what type of wood it is will help tremendously. Check the wood for rot and density. I knock on the wood, if it makes a dull thumping sound, then obviously the wood is rather soft and may rot.
Once you are sure that it is a hard, dense, and non-poisonous wood make sure to prep it really well.
Wash, scrub, wirebrush, rinse, and sand if necessary. Repeat until all soft, rotted wood, plant matter, etc are removed from the wood. I boil wood several times changing water between boils to sterilize and remove any residues, excess tannin, or chemicals that could leach into my tank. With wood that is too large to boil efficiently, I will place the wood into the bathtub and use my water changing buckets to occasionally bring fresh boiling water from the kitchen. It's worth the effort to have a nice natural piece of wood.
To help determine what type of wood it is, just look at the nearby trees or the trees found upstream, this usually helps. Woods to avoid include but are not limited to softwoods, wood that is physically soft or easily broken, rotten wood, evergreens (pine, cedar, spruce, etc.), poisonous woods like wormwood, woods in the same family as known irritant or poisonous woods (in Florida, the peppertree grows in bog like conditions and looks like an attractive piece of decor... but it is in the same family as poison ivy and people usually use gloves when clearing them from land because some people develop rashes from contact.). I would also recommend submerging the wood for 24-48 hours in a bucket, spare tank, or etc just to be sure. I never personally use wood that I cannot identify.
