For those who believe that you should be friends first?

When do you personally feel is the right time to try and introduce sex and/or romance into a friendship if that is what you want?

I figure it's about building trust. Do you love them and do you trust them? Perhaps then it's time to move on to the next step.

Like Shinu said, I think trust is very important in regards to the romantic part of things. If you don't trust him/her, then forming a relationship wont work out long term. For a FWB situation, I would imagine it comes into play as well. With that being said, by rule of thumb, I try not to pull the trigger until I've really fallen head over heels. A pretty/handsome face only goes so far, the personality is really what you'll be left with when you're dating someone long term. In my opinion, it's important to really get a feel for who they are, what they like to do, and if you feel like you'd enjoy spending the majority of your time with them doing those things.

First, it should DEFINITELY start out as friends first. Bypassing this simple first step means you're not honestly representing yourself to the other person because you're focused more on being what you think the other person wants. This is why I'm absolutely disgusted at the notion of blind dates, or when a friend is like "You gotta meet (this person)!!!" As for the "right time" to move forward... there's no guideline for that. There's no step by step procedure because no two people are the same, and no two relationships have the same progression. You can't simply put a red X on November 14 and write "Show time" on it. xD

As a few people have already said, perhaps after a solid foundation of trust has been built. Then again, if you're too impatient to build a bond first, it's not hard to find a person who is openly flippant about sex/romance topics.

It takes a little bit of time to get to a sexual relationship but with tons of communication and great chemistry, it can definitely speed up the process. Although I feel it's very important to let the other person know that you like them in that way once you figure out they're a good match for you. Waiting and waiting will only give someone else the chance you squandered!