I LOVE this game! (I've recently discovered I'm quite good at it, and have managed to get above the avvie score several times now). All the tips already mentioned are great! I score 10k+ on a regular basis, so I thought I'd share some of my strategies:
Tips:
Scoops with toppings give you 10 pts instead of 5pts.
Definitely use the cheat code for an extra life in between levels.
Stay to the middle of the screen.
You can stay directly above one column and wait until a scoop shows up there to move over a column and then back. This prevents you from having to worry about following tooo many columns at once.
If you see a strawberry bomb on the screen, and you have nothing but plain scoops, use it. Just be careful not to use it at the tail end of the level, as you'll lose the extra scoops.
As for slowdowns and speed ups: On later levels (7+), ONE, and ONLY ONE slow down can be helpful. Any more than that, and you'll run into massive scoop walls. Just keep in mind: size and speed resets to the level default whenever you get a point bonus, life, strawberry bomb, or scoop shield.
Scoops shields are wonderful, but continue to dodge scoops while you have it: this way when it runs out, you're not on top of a scoop!
DO NOT RIGHT CLICK!!! (this causes immediate end of game!)
I personally don't leave the first level unless it meets one of these conditions: 1) Gives me an extra life and/or 2)My score is over 200 (whether it be by topping scoops or bonuses)
General scores by level:
Beginning level 5 (Blueberry): around 1800-2000
Beginning level 7 (Strawberry Vanilla Chocolate): around 3750-4000
Beginning level 9 (Vanilla Chocolate Swirl): around 6200
If you can live through level 9, you should make it past 7500.
Some more in-depth guides that are helpful:
http://www.neopets.com/~PatGraham
http://www.neopets.com/~Decebuary
http://www.neopets.com/~Kallycherry
(all from garmfay's guide links)
Hope this helps!
EDIT: Oh, and turn the music off! It's cute an all, but you'll do SO much better if you have silence to work in!