So you're building a series arc, and you want to sneak something important in a few weeks beforehand. This seems like a good time to do it!
This has been done to variable degrees and with variable success in the new series. Some were just repeated references subtle or otherwise, but some proved their importance in earlier episodes than anticipated. Mr. Saxon's machinations really started in The Lazarus Experiment and the Crack stopped being a minor out-of-character curio in Flesh And Stone and played a key role in Cold Blood as well.
9: What does that mean?
So look at the clues you want to plant, the clues you've already planted, any red herrings you'd like to include.
See what you can sneak in during a seemingly unconnected adventure that will later prove to be more important than that (like the Lazarus device).
Ideally this should be a fun adventure taken on its own, with just a bit that gets carried forward to the end of the year.
This can relate to the characters and their reasons for travelling as well. The Doctor meets Amy and Rory because of the Crack, Martha's sister Tish is used to pull her and the Doctor in to meet Lazarus and recruit Martha's mother to work against them... Of course, both of these examples are the result of time working backwards, so best to plan ahead in order to work the plan backwards...
Example: The Shattered World
The Doctor, Emily and Richard land somewhere the Doctor wasn't expecting - an asteroid field where there should be a thriving planet. Here they find more evidence of the Alignment, in the stories of a galaxy torn apart by incalculable gravitic forces - an entire planet torn out of its orbit and hurled into the darkness. And someone, somewhere, has begun building a gravitic weapon...
This is an example where the travellers are (erratically) looking for something, and getting into seemingly unrelated adventures along the way. But maybe all these adventures aren't as unrelated as they look...