Just beat this game and there's a video with the details for Caravan, High Score and Original Mode. The video is iin Portuguese but despite the language you guys can see how I went though each level.
Caravan Mode: On first Stage try not dying and saving the Special Bombs for the boss. I used 1 bomb on the first Boss and got 285000 points at the end of it. Second stage is pretty much easy to get 15000 using the other bombs. Don't mind if you die, you'll get more special bombs to use.
High Score Mode: Life is more important then Special Bombs so try to beat first stage without dying and using any bombs but if you you are struggling you can use it no problem. Second stage the only problem is that half space ship top and bottom shooting than moving together to the center. Try to go to the left of the screen before they start shooting and use the special. You'll need to start stage 3 to get 600000 points. Just a heads up be careful with the small slime balls in the beggining of the stage 3.
General Tip: Don't stop pressing X cause as long as you keep shooting you are getting more points.