I learned this tip...no pun intended...a long time ago and it has been very useful.
If you don't have fancy frosting tools and tips or if you simply don't want to get them all out and have to clean them you can try this simple trick.
Take a sandwich size ziptop baggie and snip a tiny triangle off of one of the bottom corners. Be sure the bottom is flat and that it doesn't have a gusset. I have made that mistake before and ended up with two streams of frosting! aghh!
This part takes a little finesse...while loosely holding the cut bag end in one hand, with a spoon, neatly scoop a bunch of frosting into the baggie through the open end. Then seal the top and carefully twist the top section of the baggie to force the frosting down towards the cut tip.
That's it. Instant frosting tool.
Not fancy and a little more homemade looking but still tasty!
I think the frosting is the BEST part of the cupcake anyway.