Chances are you didn't play hundreds of hours on one of these like I did.
So what can you do to get good at the 360 version of this game? How funny would it be if I said "practice"? Not funny at all right? That is like the other greats bits of advice I've heard over the years like "don't die" (various games) or "you just have to feel it" (Lumines). Well you can practice all day long but unless you are practicing good habits you will never get better and your scores will continue to stay in the same range. One of the reasons you don't hear any good advice from people who play this game or other arcade classics is because they don't realize what they are doing. From the hours of practice they have developed tendencies and probably don't even realize what they do that makes them successful. So here's my own personal habits, maybe you can incorporate some of them into your own style of gameplay.
First of don't ever play on anything but Classic mode. This game doesn't benefit from updated graphics and things just get harder to see. To a new player you might see it and think, "Well there is a lot less going on here (fewer rows) so I'm probably better off learning here", but that is not the case. To be fair and make sure that I'm not just being some sort of elitist snob I went and played the enhanced version and I want someone to explain why everything suddenly explodes. If you want to see fireworks, go play Boom Boom Rocket, otherwise play this game on classic.
With that out of the way let's talk about general strategy. Now to advance the level you clearly have to kill the millipede, but if you just do this, you will end up with a crappy score and a very busy board. Listen for the audible clues for when special bugs come out. These are where the meat of your points will be so let's look at them, how they change the board, and what you should do with them.
Spider (300,600,900,1200,1800) -
The first bug that you will encounter and it can help you as well as hurt you. I read someone else in here say stay in the middle, but I can tell you that I believe that to be the totally wrong thing to do. Not that it won't get you away from the spider because it will, but because for the overall strategy it won't get you far. I suggest staying to either side, always keeping both sides clear of mushrooms. When the spider comes out, you move towards the the side he came out of, most likely under him. Never try to go over him and always wait until he's commited to going up before sneaking under him. The reason is because the spider likes to do this little head fake where he starts to go up, but then just bounces low a few times. Don't be concerned with getting 900+ always on killing the spider, it's just not worth the trouble because it's distracting you from the board. There will always be another spider as soon as you kill this one, so make it up on volume and get big scores when you can.
The spider can be your friend too though. You do not want any mushrooms inside your space so let the spider clear some out for you. Letting one spider go to clear mushrooms is a worthy sacrifice if it saves you a man (or two). More on managing mushrooms later.
Note: 1800. The only 'reliable' way I've ever had of getting this one is killing him inside of a DDT. I think you can luck into it with pixel perfect kill on your archer, but best bet is to let a DDT sink low enough that it's inside where the spider roams and nail that sucker at the same time he's in the middle of it. He must be inside of the blast radius, not roaming into it.
Earwing (1000) -
The little bugger that darts horizontally across the screen from time to time. Always try and get him if you can because 1000 points is a lot to just let it run away! Easy points.
DDT (800) -
Supposedly there to help you, but they cause me more troube then they are worth. In general if I get too infatuated with trying to get a lot of stuff into them I end up not paying attention to the whole board so what I used to do was just blow them all up right away to prevent myself from getting sucked into their trap! The best use for them is to try not to hit them until the bonus rounds and hit them then. This will hopefully catch multiples and increase the scores for all the rest of the ones you kill.
Dragonfly (500) -
These are the little bastards that zig zag down the screen in a small back and forth motion. The will lay mushrooms and just in general become a problem if they get down on you while you're trying to deal with everything else so when you hear their sound, move under them and stand still. Let them come to you, don't go back and forth chasing them down.
Mosquito (400) -
Probably the most helpful bug in the game. And high scores are dependant on successfully killing lots of them on their bonus wave. The are very predictable, they dart from one side, bounce off the other at 90 degrees and come back towards the middle. One more reason you should be on a side instead of the middle
Same strategy as the dragonfly, get in position, and let it fly across in front of you. Each one of these you kill will move the mushrooms back up one row, helping keep your work area clean!
Beetle (300) -
My personal most hated enemy. If you ever talk to me, it's not a beetle it's a ladybug! I've been calling it that for two decades now and I'm only referring to it as a beetle right now so I don't confuse people. These are the ones that come out from either side, walk across the bottom of the screen and then up and across turning every mushroom in it's path into an indestructable flower. Again, this is why you want to be on one side - kill that bugger as soon as he's out. If he came out of the opposite side you were on, then watch him like a hawk and slide under and kill him before he can ruin your day with flowers. Granted sometimes you can make good use of the flowers, but since you have no control of where they are it's best you never let them happen.
Bee (200) -
Drops down in a straight vertical drop and somehow plants more mushrooms behind it. I actually encourage you to go for these as much as possible, particularly in the begining levels. It's crucial you are cautious then though because you cannot count on your rapid fire to be there since there are so few mushrooms on the board. Stop firing, line up beneath him, then resume holding down the A button. They will continue to come until they successfully screw you with a sufficient amount of mushrooms so you can kill a good 8-10 of these before they stop as opposed to just 2-3 if you ignore them. Plus you want more mushrooms up top because that's your backdrop you are using to keep your rapid fire going. So get these as often as you can, but don't ever try and race over at the last minute to get one. Chances are you will get under it only to die, but hey at least you'll have time to see where your last arrow went.
Inchworm (100) -
He's not worth many points, but he can really save you with his slowing down the board to a crawl. If it's early in the stage I will hit him to help me clear, if it's near the end of a stage I kill him last unless he's going to make it off the board. The reason for this is because I'd rather the beginning of the next stage be slow when I'm more likely to need it. If you're really lucky then the next stage is a bonus stage and you can get off to a great start with things slowed down.
continued (because too long)...