Government Expenditure

I use 100% expenditure most of the time, only lower it when debts are running too high.

I try and keep "in the black" because you cant rushbuy if you are in debt

100% expenditure doesn't mean you're going into debt. The point is to max out spending. Then you adjust your economy accordingly. Build social improvements for morale/econ if you can't have 100% and make a profit. Trade. Trade. Trade. I could say it ten times, as you can have 10 trade routes, but you get the idea.
What do you rushbuy? It is very expensive to rushbuy things. Unless for trade goods, you are often better off putting 100% spending/100% military or social(depending on the project) rather than rushbuying. You may lose 1 or 2 turns, but you save money and all the other planets do something useful with the money that is being spent.

I rushbuy trade goods - they seem (to me) to be relatively cheap to buy versus their value.

I used to rush buy my first colony ship but I dont any more (well certainly not on the non-small maps) given you can turn them out every 2 turns anyway.

Thanks for the replies - just to be sure I have this right from what you are saying - 100% is both achievable and normal? I've struggled to get the gov exp slider above 50% which must mean I need more econ / trade? Can someone suggest the sort of things I should be building? Thanks.

I think it'll depend on your map and empire size. If LDiCesare's playing with tiny maps and rare planets, for instance, he'll have an easier time staying fully funded because the number of trade routes he's allowed will still be 10 max. The larger the map and the more colonies you have, the harder it'll be; long trade routes may bring more money, but will be harder to saturate with starbases and harder to protect.

.... from which I deduce trade is the key. Thanks for that (I haven't done much with trade so far).

Trade can be very, very lucrative. In my current game (Normal difficulty, Huge/Tight/Common), I have a "pet" two-system minor literally in my corner. I also have ten trade routes going back and forth between it (usually no more than, hm, maybe five sectors or so), plus almost all of its trade routes go to me (and it has quite a few, as I've been good about giving it tech that adds trade routes).

I then put a few econ starbases in each sector that the freighters go through, and pull down some ~6000 BC/turn in trade, a rather large part of that from the minor with some of it from the remaining AIs (it's late-game; the Yor and Altarians are gone). Even with 6000+ BC/turn from trade, and over 8000 BC/turn taxes (maybe 9000+; I've got a few econ-resource bases), I can't afford to keep funding high at all on a regular basis because my production capacity is huge (ubiquitous production facilities, near end of tech tree, fairly heavy use of starbases to boost production). But if I needed to crank things up for a while, the capacity's there; and I could get the money from the minor in exchange for tech or ships, as it's sitting on over 45,000 BC last I checked.

(Hm. One thing I haven't tried is borrowing money from it -- asking for cash up front, offering a higher amount over time.)

Fascinating - hadn't thought of that - extra capacity allows you to up production when you need it(if you have the money). The more I see of this game the more fascinating it becomes.