I can give you a few hints. The game really opens up when you get the candle. Many of those darker bushes that are burnable were modified to have slightly different graphics, sometimes, so they'd be easier to spot.
Error's Mansion: Look for bombable walls around the east end of F-1. On the upper floor, when you reach a dead end with a chest that gives you bombs, you'll be using those bombs on a piece of floor in that same room. If a single floor tile is different, it's usually a good idea to bomb that one spot.
Dam: On the second floor, look for a bombable spot on the north wall of a room with a rectangular hole. Slash every pot on the west side of F-1, and look for blocks to push.
Sand Palace - After walking down the stairs to the sands below, be sure to walk under every opaque surface. Some of them have hidden rooms or keys under them. Also, slash every pot. Revisit the basement (Not the open area under the walkways) when you get the lamp to find an HCP somewhere.
Once you have that lamp, return to the southeastern area of the overworld and start burning all kinds of bushes.
You can also get the red lamp fairly early in the Excavation if you find even only a few Relics. It's on B-2, (The green walls) which can be accessed from the southwest/west area of B-1.



