Unfortunately, solder cream was never intended to be used with a soldering iron. This can be done by moving the iron tip close to the joint for a few seconds prior to moving onto the joint. Use solder flux where possible. One of the biggest problems with soldering SMT parts is that the amount of flux within the solder core is not sufficient for the joint. However, soldering iron temperatures are far less controlled and often the flux has evaporated before the joint has solidified, leading to dry joint which is often dull in complexion.
Solder flux has other advantages too.
It increases the conduction of heat from the iron tip to joint and increases the surface tension of the molten solder. This helps to achieve a nice concave joint and minimises the chance of bridging finely spaced pins. Flux has the disadvantage that it is generally sticky, and can require special flux removers to remove. Soapy water and ultrasonic baths are one solution, but this requires a second wash in fresh water and a bake in the oven. Flux can also carry contaminants which may effect circuits operating in the microwave region or circuits with very high impedance's, especially in VCOs.