Kommandos deserve thier own tactica, but I'll try to sum it up some of the key ways to use them.
First and formost, Snikrot is amazing. There will be times to not use him, but imo if you are going to put a kommando squad in your list, he should be there. In an army that is full of maybe's and lucky dice rolls (SAG guns andWierdboyz) snikky is a garrantee. He comes in where you want him to from any table edge. He's tactically amazing as far as options he provides, and your opponent knows this and it will force his hand when he deploys, and how he fields his army after.
Having said that. One of the number one rules for making a competitive list is redundency. If something is worth taking, it should be worth taking two of. Snikrot is unique so you only get one.
As for how I field them, I take two paths depending on if I'm playing against a static or a mechanized mobile list.
Against a static list, I'll tend to take a amaller squad as I know he'll be able to get in from some edge and assault the turn he comes into play. I'm not worried about survivability as he's going to come in and one shot his target. He's an ork assassin. If it's a static guard list, I might go bigger just to deal with those huge combined platoons. Burnas are a must. If it's infantry, I can template them. If it's MEQ then I can power weapon through it.
If I'm playing against a mech list (which happens a lot since I started playing snikky), I tend to go big. I want to be able to come in from a table edge and get to cover. Hopefully he will have left me a target, but normally a mech list will consolidate and make sure nothing is within the 12" assault range he has from table edge. The extra bodies lets him move into cover hopefully, and then just flank what hopefully the rest of your army is already attacking in the coming turns. I like big shootas in this rig like Teej because you have a good chance of still affecting the outcome even if you can't come in somewhere with a target. If it's MEQ, you may still want the burnas as when you get into CC everyone can wound allocate away from them (snikky included) so that they get all thier power weapon attacks available.