I can't believe no-ones mentioned the infamous bombarding your homeworld with minerals by not having a catching Mass Driver!
But that is impossible ... Ships will refuse to remove last Mass Driver from the target planet if the payload is on route, you cant target planets without Mass Drivers etc.
Only possible situation where you can bombard your own planet is if your last mass Driver gets destroyed by ground combat/orbital bombardement with either spoilers or another empire while the payload is on route..
Or am i missing something ?
1a) Electing to eliminate ICBM's in a conventional start and then worrying about required protection levels.
Protection Level does not matter on your Capital planet and by the time you actually colonize something, you should be able to build waay more efficient and advanced PDC's.
Some mistakes from me :
Investing too much research into one aspect of the category drastically reduces overall efectivness of your ships - for example, having Tier 1 missiles ( warhead, agility etc ) with advanced engine is not always better than having more advanced missiles with slightly older engines. Or focusing on the sensors only to discover that your weapons cant benefit from that range.