I was flying a 747 and doing 250 knots below 10,000ft- then 340 knots up to approx 25,000/30,000ft- then approx mach 0.84 at approx 30,000ft and above but my airspeed only indicates around 280/290 knots how is this? I taught my indicated airspeed would be higher than this.

That indicated airspeed is correct.  In cruise focus on the mach number, TAS & Ground speed.

 

To put it in very basic terms, the higher you climb the less dense the air becomes.  So less dense air impacting the static port.

As flex stated, focus on mach. mach change over happens around 28 to 29 thousand. I fly around at FL400/FL410 and the indicated airspeed is about 258 kts. Most modern planes will automatically switch to mach when climbing through mach change over altitude.

Thanks guys