everything is somewhat easy to dodge, yet hard to dodge.
helis: lets say a spawnwar is accuring at the robber spawn, occassionly a so called 'lamer' appears, and with a quick move, swoops across the place, killing a poopload of people. after some time, i saw that heli blades, even with the worst lag, cant come threw the stone fances that are all arround the place. too hard? use the fountain. its not that hard to hear, or even look at the radar for a triangle close by.
if its on open ground, just learn to dodge it by finding an object to hide behind, even a lightpole is enough.
spas: nothing to say here, just learn to move fast. the common spas user is a newbie that cant kill nothing normally(and will probably yell ''CHEAT OMG LOL!!11!!11111!!!'') and probably cant aim eather. just run arround him till hes out of bullets, and finish him off easy.
flamethrower: i find it hard to dodge, but its very easy to kill a flamethrower user from a distance, because the flame is making its user not to see squat. use that advantage.
cars: same as heli, just easyer.
molotov and granades: now cmon, everybody knows about that trick. same way they use it on you, use it on them.