first of all, make sure you have the correct type of blade. Blades are lablled with a TPI figure. that means teeth per inch.
18TPI is for cutting thick materials, ie unistrut, angle iron scaffold tube ect.
24TPI is for cuttinmg slightly thinner materials, ie very heavy duty tray, can also be used for unsitrut, conduit, large trunking.
32TPI is for thin materials, ie most grades of tray, trunking, sheet metals.
for very flimsy materials, a junior hacksaw should be used.
Next, majke sure that the teeth point forwards, and the blade is tight.
Nest, ensure that your cutting at about 45degrees to the material, not straight across it, as your teeth will get stuck.
dont force the hacksaw, just let the blade do the work. Also, use the full length of the blade, this will mean you cut it quicker, and more efficiently.