When I was in Kuala Lumpur, the main mode of transport for me was taking the MRT & LRT. It is absolutely convenient and affordable means of transportation.
Within the city of Kuala Lumpur, the roads are very congested especially during peak hours. If you are traveling using the KL Buses and Taxis, the traffic is at a crawling speed. Therefore a lot of time would be wasted being stuck on the roads.
To familiarize the MRT/ LRT network, the first thing I did was to get the FREE KL tourist map from the Tourism Office of Malaysia at the airport. This map is very helpful to me for navigating around KL using the trains and identifying the locations and roads.
It is much easier to travel using the TOUCH N GO My Rapid KL store value train card. You can buy this from any MRT / LRT station counters. Using this card is cheaper for traveling as discount is given for each trip; as compared to using cash to buy a fare card for each trip.
The MRT & LRT network are extensive in Kuala Lumpur. It is fast, comfortable and easy to connect. Try to avoid the morning and evening peak hours; as lots of people are using the trains. The MRT & LRT is my preferred mode of transport while in KL.