I find a good way of increasing my training is to to think about how many time in a week I want to train then build them up slowly, for instence "id like to run 5 times a week" start training 30mins or whatever is comfortable then work from there. Works for me anyway
But do you mix the sessions in terms of time? E.g. 45mins, 90, 60, 120, 15.
When building up I don't too much, however worth bearing in mind one session should be longer, the real thing to work on is getting a good regular routine. Then start introducing the key session
I could work on a good regularish routine! Being able to adapt training around other priorities is key for me.
I try to do one session per week which leaves my legs dead for a couple of days, usually involving hills. I guess that is my key training.