You have to try inteval training in order to improve your lactate threshold. After 10' of jogging, just try to combine 3' sustained fast run with 3' sustained slow run and repeat till complete your usual volume of kms, after that back to calm at a very slow jog for 5'.
Do this workout once a week ( I suppose you run 3 or 4 times a week so, one of this days just do this workout), the remaining days just run softly.