These tips are by Fotis Kokkoras.
Race: Human
Difficulty: Imposible
G Size: Huge
General tactics
Do not build any colony ship until the factory counter goes to >160. With that number of factories it will take 6 or 7 rounds to build a basic colony ship. Meanwhile you have your industry up and running.
Each time you discover an advance in terraforming set all planets to build population. that means select the appropriate answer in the message box that pops up. (A nice feature of MOO1 not in MOO2)
In the early stage the rule is simple. Keep peace with everyboby, expand, and put aliens fight between each other.
I start building battle fleet when I got the MEGABOLT Cannon.
Missile bases on planets is waste of money under my strategy because the battle begins later in the game where the huge fleets are impossible to suffer any damage from missiles.
The fun begins when I discover Omega V bomb. Then all you need is two groups of small ships, each with 400-600 ships. They should be fast enough in battle to reach the planet in 2 turns. The first group attacks. The aliens fire the missiles from their countless bases. You them move the 2nd group. The aliens fire again against the 1st group. You then move the 1st group back (to save it). So the first group is the decoy and the 2nd is the killer. The 1st goes back and the second destroys the planet. If you have transport Teleporter then you only need one group of small ships. The objective of the above tactic is to destroy enemy's economy. So you must do as much damage as possible in the minimum time. I usually build 6 teams of 2 groups, so I can destroy 6 planets per turn.