True...
Ok, the biggest thing will be to memorize the enemy pattern for each stage so you know when to drop a potato bomb and really milk that multiplier. You shouldn't be using any other bombs, only the potato bomb.
The other trick is knowing when the stage boss is going to expire - they flash red when they're nearly done in - I always soften them up with potato fire as not only do you get points for each hit (which you won't with the other weapons), it's easier to control the rate of fire. If you wait until you're sure the boss is just about done and you let some of the popcorn enemies come on screen, then drop a potato bomb and kill the boss with, if timed right you can get huge multipliers from the standard 50k boss kill score.
Clear a stage of all enemies and you get a 200k bonus - so by the start of stage 2, if every thing has gone right, I should be on 1.5mil (approx).
You can rack up big numbers against the Stage 4 boss if you keep suiciding for bombs.
Suiciding to restock bombs is definitely a big strat for success on easy, as by the final boss you should have enough lives to suicide on him two or three times so that you keep bombing him for points... and still have three or four lives in stock after the 1CC.
And yes, chaining the gems is super important, but can be difficult when you bomb a packed screen of popcorn enemies, because usually there are too many gems to collect and the multiplier will reset.
Learning to use the ice cream lazer will also help with chain scores - the other weapons are pretty useless for this. Always use the potato gun to soften enemies up that take more than one hit, as you'll get points for every potato that hits - so for example, the tank at the start of stage 1 will take multiple hits with the lazer but you'll only get points for the kill.
There... does that help at all?