I tend to throw a forcefield through before any forces - this pushes away mobile ships and sets off lightning turrets (basically like Lancefighter does).
I then follow with my entire fleet though, the massed ships wipe out wormhole defenses fairly quickly and once I get them moving towards my target priority list I bring in a mobile builder, 2 science labs, 2 cleanup drones, and up to 4 engineers (to keep the ff alive). I build counter-snipers right away (though for some reason they don't seem to do anything - I never see their flares get shot out and I get hammered by sniper shots constantly - even with more counters than the # of snipers in the system). Once I have CS turrents built I build some offensive turrets - MLRS, Laser, and Snipers.
Since I tend to 'roll' with at least one leech starship, I replenish engineers 'free' and they end up following my fleet around helping keep it semi alive (took a Mk III world out recently thanks to this - highest level ships were about 100 Mk II bombers plus 2 leech star ships, 3 raid starships, and 3 starships [power boost
] - lost about 300 ships with the Mk differences but gained about 200 Mk III ships for 'free').
If the world is going to be a true beachhead (i.e. multiple wormhole connections to enemy worlds and borders a home system) I will also put in a Mobile Repair Station w/ 2 100% tugs and 1 starship tug (at least).