Requirements for wiring a sub to amp

As a complete newbie to car audio, I've done a bit of research but am still unsure if anything extra needs to be wired in between the amp and woofer in the system. I've heard of some people putting crossovers or something to ensure that only certain bass frequencies are sent to the sub, but will it still work fine if I just connect the sub to an amp channel? Apologies if this is a stupid question...

Components:  amp - 4ch 1200W max,       sub - 250W RMS JBL 4ohm single voice coil

I was going to bridge 2 channels of the amp to run the sub from (just confirming this would still be OK with the 4ohm sub load?)

Any other suggestions people would like to make about getting this setup to sound sweet would be appreciated. Cheers.

Thank you both for that - there were built in frequency cut-offs in the amp - one 'LPF' like you said which seems to make the sub only play low frequencies. I wasn't quite sure what that was for before! I've set the adjustable dial next to it to about 85Hz which is what people seem to choose from what I've seen on the forum, and the sub sounds good at that setting. Amp is bridgeable - it has a diagram on it - so I've connected the sub leads to the postitive of one channel and the negative of the other. Is it just OK to leave the other two connections empty, or am I supposed to connect them as well or something? The sub works fine as it is now though - much louder than on the single channel.

Thanks for all the hints - I've rivited the ground wire to a spare bracket on the chassis which I filed the paint off, and this seems to let the amp work well. Battery wire fused next to the battery as you say - all going and sounding good! Cheers to you both.