Hiss or hum? Hiss might mean your gainstaging needs some attention. Especially if you have pedals & effects - that's a whole big subject.
Hum - is it your amp, or the cable, or the guitar? Many stock amps are just rubbish. Some don't even use filtered DC on tube heaters. I find the designs that work best for me have the amp electronics totally enclosed in a steel box (which shields the magnetic fields). So unless you have a decent amp, hum might be a feature of the thing. An amp tech might be able to improve things - or not.
Being unbalanced inputs, you might have ground loop hum from any other components connected to AC. Use batteries in pedals, rather than adapters. You might need to use isolation transformers - once again, a whole minefield. See if your amp hums with just a well shielded humbucker guitar plugged in with a pro cable that doesn't have iron in the cable or connectors (as most do).
If you can't eliminate hum from the amp at source, you may as well shoot yourself. Never use noise reduction pedals - they are noise generators combined with tone suckers.
Gates, properly applied at mix time, might be useful. Digital editing or fader automation might be better.
I've never found noise reduction software that worked without destroying the sound. (Not that i've tried the uber-expensive stuff like Cedar Cambridge CEDAR Cambridge NR-4 Noise Reduction
Most FFT based plugins i've tried totally suck.
An idea if all else fails .... at the same time you are tracking your guitar, simultaneously track a spare channel with a noisy pickup generating hum. I have a cheap unshielded single coil pup on a cable that I use with a battery amp as a hum detector that can be used. Or a single coil Woody soundhole pup can work.
The idea behind this is that you now have an isolated track of the hum that you want to remove from your guitar track. This track is perfectly in sync with the hum in your guitar track - maybe phase shifted slightly, due to mic distance etc, but basically perfectly in sync. This means all you have to do is flip the polarity/phase and mix it in until it cancels out the amp hum. As long as you haven't messed around with compression & stuff, the phase & level relationship should be stable enough to eliminate the hum.