I did an engine swap on my GL1500. I can't tell you all the technical details found in the shop manual, but here is my advice-
Take lots of pictures as you disassemble the bike. Take pictures of hose, tube & wire routing. You can't take too many pictures.
I also used colored zip ties on all the electrical connections as I took them apart. It makes it easier to plug everything back together when you can match each connection with it's color coded reminders.
When you take a part off, put the bolts and nuts back in the holes they came out of. It makes it easier to know which bolt goes where, and less likely to loose any fasteners.
Engine removal is a big job, and hard to describe in a few sentences in a post. If you have a look at the gl1200 engine removal video in the Workshop part of the site, it will give you some idea of what is involved in pulling a Wing engine. Yhe 1500 engine is even harder to remove than the 1200.
On the 1500, some tricky areas are romoving and refitting the cooling fans and radiators.
as everyone has mentioned ,it is a big job,i know i did my tranny,yes take a lot of pictures is step one ,have lots of zip lock baggies and label them as you go,label electrical conns.as you unhook them,i started with 1 and wrote it down as i went,reason being its pretty much a reverse procedure puting it back in.a few key points 1,remem. to install the drive u-joint as you instal. the motor,good time for a thermastat,keep a close eye on all the electrical conns.as you install the engine,dont hurry ,itll go fine,PICTURES PICTURES PICTURES,they are extremely useful,good luck