Aside from better skin care, a primer is a must. I love MUFE's Matte one. As for touch ups, I read in a Japanese magazine tricks for oily skin and have loved those tips since.
For a light touch up, I blot first then lightly use powder with a kabuki brush (it fits better in my purse). For a full touch up (ie. from work to hanging out at night with friends), I use a toner spray of some sort to cool my face down. You can use Evian, or Fix+, but I use Tea Tree Water by Lush which is great and helps the blotting process a ton. Then I blot, NOT wipe, with a tissue, quite carefully.
Next, I take a stick concealer (I use the Urban Decay 24/7 concealer pencil) to touch up any places where my make up has come off. I use a Q-tip if needed, sometimes spraying it with the toner, sometimes not, to remove any smudges in my eyeliner/mascara. If I need to I touch both up.
Sometimes if I have a blemish or something and the concealer is coming off, I will use the Q-tip to remove it first then go over it with the new concealer and blend blend blend. Finally, I use powder to set it all and perhaps add a tiny bit of blush. I almost never carry my blush with me, but on oily skin, blush dissipates rather quickly and on days with important evening outings, I try to bring my blush.