The easiest way to Kistamässan from Arlanda Airport is to take the train. Take the train in the direction "Stockholm" and go off at "Helenelunds station" it is about 20 minutes ride. From Helenelund Station you can walk to Kistamässan in five minutes. Please read more about the train here >>
Another option is to take a taxi from Arlanda Airport. It should take about 25 minutes from Arlanda Airport to Kistamässan.
Take the the blue line no. 11 on the subway from Stockholm Central towards Akalla. Get of at Kista - aprox travel time 17 minutes. From Kista Centrums Subway station there is a 12 minute walk to Kistamässan. Follow the signs towards Kistamässan. The subway goes aprox 6 times per hour.
Take the commuter train from Stockholms Central towards Upplands Väsby or Märsta. Get of at Helenelunds station - aprox travel time 12 minuter. From Helenelunds station there is a 5 minute walkto Kistamässan. Follow the signs towards Kistamässan. The commuter train goes 4-6 times per hour.