Are you playing with abundant anomalies? That's what keeps my economy afloat in the early game. I even try to pump a couple extra survey ships out as early as I can, to get the anomalies before the other players do.

Also, as Mystikmind said: you don't always have to develop your new colonies right away.

I almost never trade away Logistics. That's a war tech.

This is with my spending and taxation rate both at 51%

You really want to keep the spending rate at 100% if at all possible. If, in future games, you think you are approaching the point where you may have to tick it down, reduce the number of plantery builds that cost money and put more focus on the income buildings.

In addition, for your current situation:

The money techs generally offer a boost to your economy simply by researching them. This is also true of the most (all but one?) of the government techs. The morale line of techs also provide automatic boosts to morale (meaning you can raise taxes). Don't forget to check for any trade goods that boost morale that may be within your ability to trade for...So if you can trade or research any of these, you can get a boost out of them.

Make sure you have fully developed any economic or morale galactic resources under your control. As your manufacturing tech increases, so does you ability to more fully develop galactic resources. The max is 39% with Industrial Sectors.

Sometime just before I started playing DA beta games, I switched from spending my initial BC quickly to a strategy that relies on minimal quick builds and some good luck with anomolies, as tetleytea mentioned.

I haven't tried playing above the Tough level, but I'm starting to believe that the human player is likely to be better at seeing the benefits of a short-term annual deficit than an AI that has no bonuses--I seem to be getting better results out of my colony rush efforts with carful deficit spending.

I'm not a very methodical player, but I think that keeping your economy at 100% spending over many turns is "worth more" than spending your nest egg quickly on a few planetary improvements and/or ships.

I have used credit a total of once...But it was in my current game. It was on the evil project build that adds 100% to your economy. I did the math out, and the short term bonus to my economy was enough extra cash that it was cheaper than waiting a few weeks to be able to buy it with cash. The only situation I have been able to find where credit made sense.

One thing I try to do (you don't mention what your morale is at just your tax rate) is get my morale at 70% (or even 100%). You can grow your economy faster because your tax base grows more quickly. It sometimes seems counterintuitive. But I will lower my tax rate when my spending is negative. I will run 100% production and be negative most of the time in the first year. I use anomalies and tech trading to keep things going and try to keep morale above 70%. I will usually have 4 survey ships plus my flagship running around collecting everything. When the anomalies are gone I switch them to explore. I also get as many diplomacy tech as possible and try not to trade them away I do trade the trade techs away. I figure the AI will send freighters to me as well. I try to run as high a morale as possible during the game even if this means lower production. The sooner I can build my tax base the sooner I can run 100% production.

Hope that helps

Another factor about the 100% approval / tax base is that later on you will be researching Interstellar Republic & Star Democracy. Grow your tax base early, before you research those techs. Then you get the 25% bonuses on your grown population. Lowering your taxes early will only cost you ~20bc/turn, but later on it will cost more than that just to lower tax by one point.