If it's pill form, I crush it and mix it with a dollop of plain yogurt - both Gabby and Gage love yogurt and they never know there is any medication in it
If it's liquid, I have a baby medicine dropper that I put it in, open their mouth, and squirt in the side of their mouth, near the back - goes down with no problem.
Others have posted some really great advice - some I'm gonna start using