Hey, it's really surprising how many strategies are possible with DW. My high score is 2.7 billion with only 27 loops, so there must be different strategies to get "good" scores.

First strategy - and the one I explain to beginners - was "go for multiball". Lock 2 balls in the time expander, choose Dr. #7, raise the time expander and get a multiball. Try scoring as much jackpots as possible. It's an relatively easy way to get something going on the playfield and beginners are always pleased when they get a multiball.

Next strategy was to use the O-loop to get a high multiplier. Nothing wrong with multiplier - it greatly benefits every strategy you might use to keep the multiplier up. Dr. #6 is either the first or at least the second doctor I use. So the multiplier is raised two steps instead of one.
Sonic booms are nice, but it takes some skill to get them. Until you get a sonic boom, there's only those lousy millions in the O-loop. And seriuosly - at 4x multiplier that's only 250k multiplied. Not really worth the effort.

3rd (and current) strategy - go for video mode. Dr. #1 is usually my first doctor. The shot to the left of the time expander is easy and repeatable. Hit the TARDIS three times and you're ready for video mode. Lock the ball in the time expander and switch Doctor to #6. Try to raise the multiplier and start the video modes by hitting the TARDIS again.
In the 3rd video mode, there's an extra ball. You also get another doctor with each completed video mode. Plus some 20+ mil. extra points every 7 doctors - even more if you get 7 doctors with one ball.
Even better - on your way through the loop, you actually do something good for your score along the way. You casually hit repair targets, giving the occasional million and raise the transmat score in the bumpers, giving you extra doctors or a few 100k points when hitting the transmat target.

So my strategy is #1, #6 and then it depends on the ongoing game.

A few weeks? I feel clumsy and ashamed.