Bring a hoe, use it to flatten terrain to help avoid leeches and makes paths for easier navigation.
Don't go in at night and enter slow, picking off as many baddies as you can with your bow.
Use trees for cover from archers.
Keep an eye in the waters for scuba skeleton archers.
Fall back when you need to.
Blobs aren't that bad...they can only hurt you when withing a meter or two.
Blunt weapons are good for most swamp baddies.
Keep poison resist potions up.
The locked things you're looking for will have a green torch burning out front.
Not all swamps will have these locked things so don't spend a lot of effort to build an outpost until you find some.
If you can, scout first from the sea or higher ground of the biome next door where your visibility is not impeded by the swamps gloom.