There are 4 main ways to make combos::

1) Do a charging attack then a standing attack. You can do a charging attack (like NoMoment) then a standing still attack (like Doubleslash) and they should connect well.

2) Cast 2 spells of conflicting schools. Spells of opposite elements seem to connect extremely well (shadow and light, time and space, etc.)

3) Use the same spell/attack twice in a row. You can actually do a combo of 5 swallow swings.

4) Add onto already existing combos. Here are a couple of things you should know. Fist is THE best combo linker, Life Sprinkler is a good finishing move, and Turbid Current is an excellent move to start combos with.