How many Mortal Instruments books do you need to read to understand the Infernal Devices?

[moeglisaweise]

For context: my boyfriend started reading all of my favourite books and even though i love the mortal instruments its not so dear to my heart as the infernal devices, also i think he will like tid more. So how many of the previous series does one have to read to get everything from tid (except the epilouge of course thats not that important)

[Magnus Iskander]

Interested in the answer too! I've read TMI many years ago, and frankly wasn't too impressed by it. However I've heard wonderful things about the The Infernal Devices.