Done this about 2 years ago.
Hardest thing is to find exactly what you need to do, like Uncle says,. before you even start on this road i suggest you do that, and get it in writing, If you can luckily for me i did, as goalposts grow legs and move.
Here was my situation.
2000TT, 1200 Multi crew, 500 jet, 1100 Turbine.
I did all 14 exams, the radio license test, and after my Initial Type rating in a mulit crew aircraft i did a LST with a Flight Ops Inspector from the CAA in teh aircraft, they will not travel abroad, bear in mind this takes 3 months to arrange, and make the plane as big as possible, as i was told by a lady FOI at Gatwick, sorry we dont do little planes, only big ones, despite mine having a 3000 mile range etc.
Good Luck