I a sorry bu by the questions yu are asking, there is no way in hell you have ever i.v`d , let alone injected "for like, 4 years". Thats a giant load of bullshit. Not to be mean, but i hate it when people arnt honest. We cannot help you if you dont tell the truth. You are no more a past iv user than i am a pornstar......
You need to somehow manage to get that needle in at roughly a 45 degree angle. Make sure the bevel is upwards facing you, this is so when the needle is in, and you draw back, it doesnt just suck the vien wall into it and not give a register.
I have t agree with Captain heroin that you should just avoid iv use if you have a tremble. You said you had one surgery, which indicates on side, if you were tellin the truth, you would just switch and use the other arm.
Just please realise with the questions you are asking, it is blatantly obvious you have never injected before.[Thats a great thing by the way]
Its pretty hard though to master the art of injecting when one has a tremor.