Chris and I are very lucky when it comes to the first bullet point: we have similar styles and taste when it comes to fixtures, furniture, colors, patterns etc. We both like oil rubbed bronze (and brushed nickel), we both like paisley, we both like traditional and modern styles (weird I know, they couldn't be more different)....you get the idea.
When it comes to the second bullet point, Chris is a lot better at compromising than I am (when my parents were potty-training me and it didn't work so well in the beginning my dad told me my great grandma said, "that is a willful child." That really hasn't ever gone away).
We have worked out a great decorating/product purchase system:
1. Establish who cares more.
This may vary from product to product (one cares more about paint color, the other more about furniture). In our case, most of the time it's me, though Chris tends to care more when it comes to furniture finishes, or wood built products like cabinets, side tables, etc.
2. Find out if the other person has any specific preferences, even if you care more.
So, we've established that I care more, but it's important when I start to research a product that I need to know if Chris has certain things he wants me to look for. For instance, when I was looking for our sink faucet, I knew Chris wanted one that poured water from a bit higher than most do, so I made sure to weed out all the ones that poured out water from a low level. If your partner doesn't care at all, that makes the next step A LOT easier
3. Research and find a number of items you like
For whoever is more interested in the product you're looking for, go online, to stores, friend's houses, etc. to find a number of examples of a product you would want to buy. For instance, when I recently looked for a ceiling light for our bathroom I scoured the web and came up with about 5 lights that I was interested in and wanted to purchase.
4. Share those items with the other person and let them pick their favorites
When I came up with my list I compiled the items in an email as a link list with little notes about what I liked about each one and sent it to Chris. He looked through all the lights I liked and picked 2 or 3 that were his favorite out of the ones I selected. Sometimes he'll include something he found that he really liked as well. Most of the time he'll also include notes about which ones he likes for what reasons. Then he sends the email back to me.
5. Pick your favorite out of the ones your partner revised
Once I've got his revised list, I pick my favorite based on my notes, his notes, practicality, price...you get the idea.
This plan has seemed to work really great for us. Like I said before, we're lucky because we have pretty similar tastes and we defer to the one who knows more/cares more (although sometimes I don't defer to Chris when he knows more - which is frequently - but like I said before as well, I'm a "willful child.")
What I like the most about this method though is that more weight is given to the person who cares more - which I think is fair - but it's still a joint decision because the other person gets to revise the list, throw in something that they like and then the final decision is a good representation of both of your preferences.
There are always uncontrolled variables that get thrown into the mix:
6. Got a debate? Make your case. And take your time.
Sometimes one of you may feel REALLY passionate about something that the other person may dislike. For instance: when it came to our kitchen hardware I desperately wanted glass knobs and bin pulls. Chris was NOT a fan of the glass bin pulls and I had to endlessly convince him why we should get them, why they made sense in the room and house, and why I liked them so much. We talked about it for a long time and held off on the decision for a while. Ultimately Chris gave in because he saw and understood how much I really wanted them and was a great partner and let me get them. To this day, they're probably the thing we get complimented on the most in the kitchen
7. Learn to give in and let the other side win.
Chris let me win that last argument because he saw and understood how much I wanted those bin pulls and realized that while he didn't really like them too much, my desire for them far outweighed his dislike for them, so he let me get them. VERY gracious and nice of him.
8. Remember when...
It's important to remember those times when the other person let you win. A similar debate came up a little while after we got our kitchen bin pulls when we were deciding what kind of Trex we wanted to get for our backyard decks. For some reason, I have an irrational hatred of the color red (although growing up in Berkeley and going to Cal games when I was little I'm sure aided it). But Chris really wanted the Brasilia Cheyenne Trex finish, and I liked the Espresso finish more. But, I had to realize that the decking was more important to Chris than it was to me AND he let me get the bin pulls I wanted, so it was fair to let him win this one
Those rules have really helped us get along during the renovation. There are times when we want to smack each other upside the head with a hammer for other reasons ("No, I don't know what you mean when you say 'that tool that does that stuff over by the thing,'") but generally speaking we like to keep things pretty fair and balanced over on Picardy, and these steps seem to do the trick for us!