I did the Ghosts 'N Goblins speedrun linked up there /\ and recently got into high-scoring this game. I won't add my score to this challenge since I'm not part of the community, but I thought I'd add some helpful techniques I've built up over the years. Some are obvious, but included for completeness' sake.
-Get a knife.
-All of the shorter, crooked tombstones can be shot to bring out a 1000-point ghost. You have to shoot him quick when he's vulnerable though, so try to time it instead of button mashing (or else frog)
-The zombies always come up 3 at a time. If you kill 2 and you can't see any more, then watch out for one running in from the side.
-If a zombie drops a point bonus, but it's on a tombstone that you can't walk through, then jump on top of the tombstone and walk off the side to get it.
-Go up the first ladder and get on top of the first tombstone to the right. Then jump off it towards the left. 10,000 point item falls.
-A good Red Devil technique that works for almost all of them is to shoot it twice while it's on the ground, then run away from it, then jump away from it as it swoops and shoot behind you. Usually he won't be able to hit you that way, and you can just keep doing that until it's dead.
-Jump as soon as you get off the raft on the other side for some extra armor.
-Duck down as soon as you see the flying knights appear and wait for them to pass by, they can't hit you.
-Jump in the middle of the next ground after the flying knights part to get a 5000-point item.
-The boss can be killed by doing the jumping-away, shooting-behind-you thing.
-The blue devils always come out of the same spots, so you can get used to where they appear and have a better chance of getting through.
-Keep to the top of the first section to have a 5000-point item fall.
-The best thing to do at the orange building with windows is duck down when a ghost comes at you, because when they hit ground level they are flying too low to be hit by a standing shot.
-The ogres should be shot with good rhythm and not button mashing, it gives them less time to move and throw spike balls.
-Keep the birds in mind all the time because they like showing up as soon as you're not paying attention.
-Extra armor is got by jumping in the very top-left corner of the ogre town.
-Don't go to highest top-right spot on the ogre town or jump during the second-highest floor, or else you risk a torch dropping in your way.
-Ride to the top of the part with 3 platforms to get an extra-time item drop.
-The first of the 2 bosses will jump to your left quickly, but you can usually hit him 3 times before that. Remember that their shots can be ducked under.
-The two-faced tower monsters can only be hit when their faces are showing. Both the high and low projectiles can be jumped over, and neither can be ducked under.
-The least number of Red Devils you'll have to fight is 4. The first one you should shoot from far away, then do the jump-away technique. The second one is easier if you shoot twice the moment you jump onto his level, then walk towards him a few steps so you won't jump off the edge when you do the jump-away.
-Go up the ladder after the area that looks like stairs. Go two platforms up, then jump back off it to the left for some extra armor.
-For the third Red Devil, shoot him twice when you are at his level, then jump straight up and shoot 2 more times and once more when you land, he should be dead. Jump off the right side and you should get a 5000-point item drop. The fourth devil is at the bottom once you jump down the right side. You do pass one on the way down, but as long as you don't shoot him he won't come after you.
-Don't get the red and white king statue, he turns you into a frog.
-If you have a Lance right now, grab the Torch. The Lance doesn't affect the stage boss, though the Knife is fine.
-If you happen to fall onto the area with the extra life, kill yourself and start the level over. The platforms take too long to become useful for getting back up and over.
-Try and hit the Red Devil as you're jumping over him.
-The blue devils always appear in the same spots.
-Jump over the fire columns, walking's no good.
-The first king statue you come across is a frog. Jump to the right after that one and you'll get the real one to drop, for 10,000 points.
-There's an extra life and a 5,000 point item on the very right side of the stage, in the middle. Just climb the ladders over there to find them.
-There's extra armor when you go over one of the eyeball platforms. It's on a required-for-completion path, so just by trying to beat the stage you'll run into it.
-The stage boss can't hit you during a swoop if you're ducking. Be careful not to duck on a ladder.
-Shoot a couple times when you get up the ladder, then move gradually to the right while shooting to the left to kill the cyclops miniboss.
-Stand under the head of the dragon, then when he starts to move, jump left a few times while shooting right. Then when he turns around to fly to the right, jump right and shoot left.
-A shield drops here. Pick it up if you want to beat the stage and start over at Stage 1 on the second round, otherwise beat the level with any other weapon and it'll set you back to the beginning of Stage 5 without losing a life. This is banned at Twingalaxies if you do it too much, but I hear this place is more relaxed.
-This boss is too easy to give any strategies. Just jump to hit his top face. Also, this is the only stage where Arthur can moonwalk, so use that as you see fit.
Round 2 is a lot like Round 1 except the enemies and projectiles all move faster, and the Red Devils shoot more fireballs than the Round 1 guys. The bonus-point item drops are all the same.
Ask me if you've got any more questions, I need to unload all this GnG research somewhere, after all.