I'm still learning the 2008 game, but I've already beaten all the Republicans in the Campaign Game and am ready to face the highest level (JFK) as a Republican, so my tips are probably worth something. I'll focus on consultants in this post.
1) Using consultants correctly is key. Note that the consultant, intimidator (and  in a different way the webmaster) function on every turn, cumulatively, whereas the spindoctor and smear merchant only affect the instant of a calculation. A consultant acquired on Turn 2 can add 160 points of awareness over the course of a game; the intimidator can subtract 200 from your opponent. So load up on these guys early. Spindoctors and smear merchants can be purchased late in the game, subject to the limit of 2 purchased per turn, and placed in the most valuable undecided states. I start my consultants in big fundraising states to get awareness up to 100% in California, New York and Texas early. This will increase fundraising yield. Then I shift these guys to small states with more members of my party; they can raise awareness there 4x as fast as a campaign HQ, and can be shifted around at no cost from turn to turn. A bevy of intimidators placed in California can really do some serious damage to the AI's plans. Place webmasters carefully in states which are a) valuable swing states; and concerned about issues which you will want to take national with TV ads. Once you have a webmaster supporting several ads, make sure you have enough points in reserve to replace him immediately if any opponent's fixer zaps him. (Otherwise, you'll find your ad bill suddenly multiplied.) Don't use fixers to eliminate opponent spin doctors or smear merchants until late in the game. Use them instead on well placed consultants/intimidators or special assets acquired by luck. If you get a Money Man, don't place him until you are ready to use him, then use him to fundraise like crazy before a foe's fixer can take him out of the game. I buy the single PR man, speechwriter and fashion consultant early, so my candidate can benefit from them throughout the game. BTW, I invest immediately in a top-level consulting office; 7 consulting points per turn give you a big edge.

Note also that the same distinction of cumulative vs instant of caluclation effects applies to some of the special units. A Hollywood Friend, for example, has a cumulative effect like a consultant, and should be employed at once and moved around. The media darling, on the other hand, should remain on your clipboard until the final game turn, when she can be deployed most wisely and not get zapped by a fixer.

Here's a tip on question marks: It's hard to beat the AI to a question mark, but if the AI has finished its moves with a question mark remaining, wait until the end of your turn to go there, so that the frequent time wasters will have minimal effect. Always go to the question marks , however, unless they appear late in the game in a closely contested state you must have to win. In the latter case, only go there if you are behind and need to roll the dice.