As I had some lovely (and more expensive than usual) fabrics for this coat, I wanted to treat them right. Since I asked for a lot of advice and googled a fair bit, I thought my findings might be useful to others.
Starting with the outer fabric which is a wool blend - 90% wool, 10% poly. This is a good combination for me as I am sensitive to 100% wool A lot of people can get away with wool in a coat as it doesn't sit against the skin but I particularly dislike it against my neck and this coat has a collar so wool blend it was.
After a lot of googling I found 3 main methods for pre shrinking wool. First is taking to the dry cleaners. Easy but pricy so not for me. Second is steaming with the iron (as Tasia did here). Simple but time consuming. Thirdly is this method outlined by Pam from Off the Cuff (this is a link to her new blog but her old one here is a treasure trove of tips, especially for shirtmaking). To save you a click, you wet large towels with hot water and put in the tumble dryer with your dry yardage. That's it!
I was concerned about trying this with my whole yardage so I tumble dried a swatch first for the recommended 40 minutes. There was no obvious change to the look of the fabric so I put the whole yardage in the dryer with 2 damp (wrung out as much as possible) bath towels. It worked perfectly - but if you do this be careful taking it out of the machine as it was still boiling hot! A quick press later and my wool was ready to go.
The lining is viscose acetate. I had planned to wash as normal but when the fabric arrived it had a dry clean only sticker on the tissue it was wrapped in. I considered not prewashing as I plan to dryclean the finished garment but advice from the lovely Claire Louise from the Thrifty Stitcher that it's really important to pre wash linings as even a bit of sweat can cause shrinkage. So I decided to put in in a delicate wash and it came out fine. Another great tip from Claire Louise was to iron it damp to get the creases out properly. This worked brilliantly and not sure why I haven't tried it before!
This just left the interfacing. I ordered Speed Tailoring from Gill Arnold on the advice of Anne from Mercury Handmade and it came with really detailed instructions on how to pre shrink, which I have never done with fusible interfacing before. I soaked it in hand hot water for 20 minutes, rolled it up in a towel to take out excess water and hung up to dry. When applying, Gill recommends a steam shrink, where you place the interfacing on top of the fabric and steam from a couple of inches away, smooth out fabric and interfacing and then press using a press cloth to adhere. This method worked really well and the interfacing is really lovely stuff. It stabilises without stiffening and adhered perfectly and easily to the fabric.
Hopefully some of these tips might help if you are making a coat in future!