I see a lot of people on here converse about backfires. Personally, I feel that if you fear backfires & doing particular spells or ritual work, You will only increase the chances of a "backfire." Remember, Magick all starts in your head! And to be quite frank, You should have no reason to worry of backfires if you know 100% what you're doing & have adequate knowledge on your practice. Sure, there may be trial & error. However, That's why you stick to the basics including protecting yourself, until you have more experience on spell casting in general.
Honestly, I have found that the practitioners who have backfires in workings are those that go into a working fearing a backfire. Thinking about the working going wrong only pollutes your mind and energy when doing the working, making it much more likely that your spell will backfire.
Some people consider negative workings more likely to backfire but in my experience all workings are equally likely to backfire if you have the potential for backfire in your mind while doing the working. Some workings are also more likely to backfire if the person the working is aimed towards has stronger protections than your working can deal with, but this is not very frequent.