VERY slowly and as blown up as you can get it.
If it's a register where the handwriting isn't great then I would just spend a little time looking at just one page.
Take your time getting familiar with the person's handwriting.
Find names that you are sure of, say you find a John and you can see how the person wrote it, then you know how he wrote each of these letters.
Then find another name that you are sure of and mentally take note of how he wrote each of those letters.
If you then find a record that you think might be your ancestor but are having difficulty working it out, look back on the handwriting on other records that you are sure of and start to cross reference each letter.
Hope that makes sense

Tara