I have just beat Outpsot 1.5 on its hardest level (and in three hours, I might add). Thus, I feel somewhat qualified to answer this.
Okay, first thing I do is look for a place to land with the greatest concentration of clear terrain, and in such an area look for the nearest mine. Now land the seed factory one tile north and two tiles west of the mining beacon. That way the seed factory smelter is right next to the mine. After you have the seed factory down, RoboMine the beacon, and Robo-Doze terrain next to the "open" ends of the tube intersections. On one of those ends put a Robo-Digger to work. This will allow you to have underground structures.
So, eventually you'll get to land the colonists and cargo. Land them anywhere that won't possible be in the way, but within comm range of the seed factory. Turn 12, you must have your Agridome and CHAP built.
That is a start. I recommend that you read the documentation that comes with the Outpost 1.5 CD.
