I'm just starting on a new base after 2 failed. Any advice on how to better protect my fortress? E.G. Don't flood your base ETC. (I have only been playing DF for 3 days,Including today).
Walls are your friend. I have an entrance or two with a few cage traps behind raisable drawbridges - a no-brainer as they capture plenty of animals and act as an early warning system for goblin thieves etc.
When sieges come, I raise the bridges, forcing invaders through my trap entrance. I now have a bank of compact automatic drowning chambers (driven by river water / gravity) which fill up with dead goblins. Down below, one lever per chamber dumps remains into a level with storage and magma forges for melting objects nearby. I set it up so I can use one of the drowning machines units to dispose of caged enemies too, with only one lever pull to release the cage.
A good basic to know is the hatch/pressure plate combo :-
XHX - Hatch over channelled ground (make sure there's no ramp there though)
XPX - Pressure Plate
X = Wall
I guarantee nothing that walks on the ground will get past that (from the south), even stopped forgotten beasts (though they broke the hatch, leaving a hole in the ground), but your dwarves will go straight over it (set to trigger by creatures, minimize low weight setting and make sure it's set to no citizens trigger)
EDIT : Can't help myself - this is my drowning machine design (one tunnel worth) each line has walls to left and right:-
O - outside / entrance to trap
R - a ramp up (goes to the 'O" outside / entrance to trap). Enemies enter down ramp
H - a hatch
P - a pressure plate set to trigger by creatures, set minimum weight to lowest.
H - a hatch
B - a 1x1 raising bridge
G - a floor grate, for drainage
I - path leading inside base, more cage traps here just as a precaution.
Directly above the pressure plate is another hatch which holds back a torrent of river water. All 3 hatches and bridge are linked to the single pressure plate. 1 level below the hatches/pressure plate is a 3x1 retractable bridge (lever operated). the goblin drowns here. and the lever dumps the goblinite remains down another level into the workshop. There are grates in strategic locations to let the water flow away.
This design has killed 40 goblins in a row without fail. They hit the pressure plate, opening the floor hatches so they can't path back or forward, water instantly dumps on them washing them into the hatches. The raising bridge so far is just a precaution to drown them even if they are not washed away, while ensuring the water drains away. So far not one goblin has managed to stay on the pressure plate.