There are actually three things you need to take care of when transporting signals over long lines that are likely to pick up noise:
1) - Use low impedances
2) - Add an input (low-pass) filter
3) - Re-shape the original signal

An additional fourth point may be to use some sort of galvanic separation of the sensor supply to prevent your MCU signals and power to go into the field, but that's another issue.

I think all of these three have been mentioned to at least some degree. However, the combination of the three is essential for proper signal transportation under bad conditions.

Obiously, the parameters of your design will depend upon the type of signal you're working with as well as the bandwidth you require. And not everything needs to be done in hardware - you ARE using a micro, aren't you? So use it for over-sampling and/or filtering and make use of Schmitt trigger inputs if you have them! For normal digital I/O you may end up adding not much more than a few resistors and one or two capacitors to do the required job.