Sometimes you might be interested in someone but since you have never met or engaged in a conversation, it becomes a challenge to communicate. However, you can still manage if you take the following steps
A comment about something in that environment
If you are in a matatu travelling to some place and she is seated right next to you, don't panic just talk about anything like for example "these car's seats are really rugged", notice how she will respond, tell her about how this vehicle's conductor was busted by the police the other day. If you sound funny to be sure that she will join in and that is how you will start getting along.
Find a common interest
When you are talking make sure to notice what makes her interested. If she is seated alone ask about "How do you see this event?" If you are traveling, ask her whether she likes the music that is playing. Once you have found what interests her, be sure that now you will get along well.
Be confident
When you start talking to her make it look like you know her very well. Ask questions confidently and when you are giving an explanation do it like you are an expert. However, if you do not have a clear information about something, be honest to say you don't know, that is how a confident person behaves.
Remain interested
Approaching her in the first place shows interested but you need to continue showing that you like her and out of so many you have taken notice of her. Talk about her style, compliment her. This will see your first conversation with her become a stepping stone for many more to come.