What tips work depends on what you want to do. Notice for example that custom candidates can be either your presidential candidate or your vp - you can really shine with 2 customs so that each has 10 in half the stats and 1 in the other half, because for most of them (ie experience) only the highest stat counts.
TV ads are great, but you need to decide whether you're mostly trying to influence the state or the whole nation. Ads create a national improvement to your position on an issue when they're created, but only improve national awareness (and your issue rating in that state) if you leave them running.
On HQs: level 1 and 2 HQs pay for themselves after 25 turns (25*10k=250K, 25*30K=250K+500K) but level 3 HQs pay for themselves in 20 turns (20*90K=1.8M, cost is 250K+500K+1M=1.75M).
I find webmasters to not be all that useful; you can affect one state cheaply with a webmaster by keeping tv adds running, but I'd much rather have a movie director to halve ad creation costs. Put him in an enemy stronghold, then spam tv ads and remove them the same turn so the money keeps flowing in. That state will be yours quickly just from the ads' initial effects, and you'll maximize national issue change per dollar spent.
If you're pursuing the HQ investment early on strategy, build up political capital when you run out of money. If you don't spend it until the last couple of turns (preferably on endorsements because they effect the whole nation), the whole nation will be against you most of the game but your opponent will not be able to plan and counteract your endorsements because he won't see the effects till it's too late. Seeing the whole country turn your color after you blow 40 capital and get all the endorsements at the end rocks.
One more thing: as far as I can tell, all democrats try to spam environment ads in california if you fight for it. consider establishing one tv ad there early on to give you the momentum on that issue and to make fundraising there easier due to higher awareness.