I hate to contradict Messiah but the purpose of not collecting taxes before a jump is not just the interest it's mostly about the way taxes are calculated, you should always pay the bills and not collect taxes before buying the infrastructure.
This is because the tax/bill system is pretty simplistic. Your bills or tax collection are based on your nation stats at the time you click the button, they are not calculated each day based on the stats for that day and then added to the amount from the day before.
So if you are due to collect 20 days tax it will be calculated as current tax per citizen * current population * 20. If you buy a lot of infrastructure before collecting the tax your new citizens will also end up paying tax for 20 days giving a large boost to the tax you collect. Think about it, if you add 2000 citizens paying $50 per day that is an extra 200,000 per day or an extra 2 million on your 20 day collection.
That doesn't take into account the effect of any new improvements that you buy. In my simple example you would qualify for 2 new improvements, and if you added 2 stadiums they would (in the case of my nation add 50,000 each per day). So now my daily collection would be approx 300,000 giving me an extra 6 million if I collect tax after buying the infrastructure and improvements.
Bills work exactly the same they are based on the infrastructure, soldiers, etc. at the time you press the button to pay them, so always make sure you pay bills before a major increase of infrastructure or you'll end up paying a lot more.
Now the improvement cycle.
Between bulk infrastructure purchases always have 3 schools and 2 universities if you are a tech dealer as this gives you a 20% discount on tech and the rest should be revenue increasing (banks, stadiums). If you are not tech dealing then look at either revenue increasing or bill reducing improvements depending on what you are doing.
Before buying infrastructure, try to get as many factories as you can even if this means dropping some other improvements. As soon as you have purchased the infrastructure destroy the factories. I know this sounds like you just threw away $750,000, but again, look at the math.
The 5 factories will reduce infrastructure costs by 8% each, for a total of 40%. If you are buying a lot of infrastructure this far outweighs the $750,000 you "threw away" on factories. I'll use my nation as an example I have 1,920 infrastructure, now lets assume I have $10 million I'm going to spend on infrastructure. I'd have to pay approx 46,000 per infrastructure point assuming no resource bonuses. My 10 million would buy me 206 points.
Now suppose I scrap 2 Universities and 3 schools and buy 5 factories. The factories cost me 750,000, and buying back the schools and universities afterwards will cost me 615,000. So take $1,365,000 away from my 10 million and I have $8,635,000 to spend on infrastructure, what will this get me ? Well my starting cost for infrastructure is now 27,645 per point so I can get 291 infrastructure points. That's 85 extra points.
Remember that the more infrastructure you start with, and the more you are buying the bigger difference the factories will make.
If you are involved in tech deals always ensure that after you buy the infrastructure and are buying improvements that you have 3 schools and 2 universities to get your 20% discount on tech, and remember schools and universities also improve income, so you are scoring both ways
Now you are at the point where you should collect your taxes, and can then start the cycle again.
Hope this makes things a bit clearer.
Zeph.