It has been kind of dead here so I wanted to contribute. I started training again after taking a year off. I'm gassing out after 3 rounds of sparring but I was happy that I regained much of my skills after week 1 of training.

I'm not really qualified to talk about super advanced stuff. Here are two simple tools that I like to use sometimes.

Walking punch
-One-two combo or one-two-lead hook combo, then slip or bob/weave as I step in the direction of my last punch. I like to drill this off of a slip or b/w where I end up moving forward and to the side. Partner moves back out of range from a counter.
-Since he is too far out of the way to counter from that position, push off with my lead leg as I punch with the same arm (last punch thrown). So basically, push off with the same side leg as you are punching, and step forward with the opposite
-'walk' and punch like that for 3-4 strikes. As you step, make sure you move your head with it (same side as the foot stepping forward). This basically helps cut off your opponent from circling out.
-chase your opponent if you have to. This is a very agressive move. I like to end with a kick.

Notes: careful not to overcommit and overextend.
This is how I drill it, but it comes in handy in many other situations.

Basic 'circling out' or fighting retreat
I see this as the nemisis of the walking punch. But really, works great against almost any straight-line attack.

-the retreating jab, lead side: step back and out half-step with your lead leg. As you step back with your back leg, positioning it to a fighting stance, when the back foot hits the ground, lauch your jab. Practice it counting 'one-two-one-two'
-same, back side: start with your back foot stepping back and out. When you drop your lead foot back into position, launch your jab.
-Drill: partner holds up glove or pad and agressively moves forward. chases me as I circle out. I retreat while landing jabs onto the target, beating his chase. Mix in straight and uppercut, finish with kick.

Maybe this belongs in the beginner's forum.