En réponse à Trebor Jung :

>How do you write diphthongs - as (e.g.) /ai/ or /aj/?

The true standard way is /a_i/ (the underscore corresponds to the IPA 
tiebar) which differs both from /ai/ (two vowels in sequence, but without 
forming a diphtongue) and from /aj/ (a vowel followed by a consonant). But 
many people use one of the ways you describe, when no confusion is possible.

>How do you write voiceless nasals, e.g. nasalized /p/ and /t/?

With the voiceless diacritic _0 on the nasals :) .

>How do you write retroflex consonants?

This has already been replied in length :) . Note that IPA has specific 
characters for those.

Christophe Grandsire.

You need a straight mind to invent a twisted conlang.