Basically you have to understand the language itself, and manually decipher each command. As you know, Famitracker regroups volume, arp, pitch and duty all into a single container called an 'instrument'; MML keeps those things independent from each other, as there is no 'instrument' command per se.
This is the reference I used when I first tried to learn the MML language. It's been pretty useful, but now you even have the luxury of having tonnes of great examples available online for reference.
Basically, here are the most frequently found commands for 2a03 (as well as other chips), other than the notes themselves of course:
@# = static duty cycle (the values correspond to Vxx in FT, i.e. @0 = V00, etc.)
@@# = calls a predefined duty cycle envelope (look for it in the macro definition section, usually below the header). Duty envelopes are defined using @#, but are called within a track using @@#.
v## = static volume
@v## = calls a predefined volume envelope (again, look below the header)
D## = detune (works differently than Pxx: D1 = P81 and D-1 = P7F).
EN## = calls a predefined arp macro. Arp macros are relative, rather than absolute (like they are in FT), so be wary.
ENOF = stops a previously activated arp macrp
EP## = calls a pitch macro.
EPOF = stops pitch macros
MP## = calls a vibrato macro.
MPOF = stops a previously activated vibrato macro.
