I think it was two things, complete paperwork and good proof of the relationship. She was not even asked to go to Moscow for an interview.
Obviously there are many things that can slow things down, but if your just a regular person in love with no criminal, medical or other strange issues than you only have 2 things to worry about. Making sure you get everything in the application, and the proof.
Read all the guides, all the forms, and even see how much you can fill out right away. Make sure you understand what they are going to ask you and what they will consider. If you don't realize that they can suspect your marriage is only for immigration and rush things or skip things to make things faster, it will look more and more like that is true.
For instance...once we were engaged and planning a wedding, we also started to look at what the paperwork for immigration was going to ask us about. So we knew they asked about meeting each others families, about the reception and who was there, about the honeymoon, wanted photos for proof, etc etc.
So when I met her sister and her boyfriend, we had pictures. Met her parents, pictures. Met her son, lots of pictures of us doing things together. Nothing was staged of course, we were doing these things anyway, we just made the camera and photos PART of everything we did together. Every visit we had we made sure we had pictures of us together. If you are looking at a famous landmark, get a picture of yourself in front of it. This gives you lots of photographic proof to choose from to send. More proof is good. Spend $200 on a camera now...or spend $$$ on a lawyer later.
During the planning of the wedding because of distance and costs no one from my side of the ocean would be able to go. Also because a wedding and reception is expensive AND I had to fly over for it too, we were considering skipping the honeymoon. I know many of us have thought of that or even did that. My wife was worried that they specifically mentioned honeymoon in the forms. Worried that they were looking for that. I thought about that a lot and came to this conclusion...I would rather spend money and a few weeks time NOW, on a honeymoon, than to have our marriage look less legitimate in the eyes of the CIC. So we delayed the wedding to save more, and we had a wonderful honeymoon. Honeymoon = more proof.
And remember...if you visit...KEEP everything. Passport stamps and airline boarding passes are physical proof you have been in the same place.
And then sending it all in. I didn't send it ALL. We had a lot. Months and months of chat logs. 400+ different email threads. 100's of photos. Phone bills. I sent them a month of chat logs...and explained I had 10 months more. I sent them the titles of the 400+ email threads and explained that I would print off the actual emails if they wanted but it would be several hundred pages. I sent them 50 photos of us together on different visits or with family and labeled them all and explained I had another couple hundred if they needed. They got to see a lot of proof...and if they read the notes, they knew there was an even larger stack of proof sitting here waiting.
And finally, do some preparation to be together. Maybe you need to add your spouse to your dental insurance plan? Make them a benificiary for your life insurance. You should get a letter from your company plan showing that...send that in too. Perhaps even a will with them on it. More proof!
I understand many people are already applied and just waiting, but maybe some people are engaged and here looking for ideas and I hope this info can help them. My philosophy through all of this was...I would rather spend money and time on things for us together now, than spend it on an appeal and lawyers later. Think about it...take 2 extra weeks together and spend some money on a honeymoon OR skip that, be found by CIC to be not a real marriage, and have to spend many more months and much more money on lawyers. Do everything you can to avoid the proof issue and hopefully it can go as fast for you.