Like basically everyone else in this thread I am going to strongly suggest you don't start IVing. It has gripped my life for over 7 years since I first did it at 21 and made the mistake of my first meth use and first heroin use both being IV because I was in a rush to ruin my life.
I am now heavily addicted to the ritual and the ROA and find it impossible to go back to any other method of using unless I cannot hit myself and need to plug instead.
There are guides online showing you how to IV, and YouTube HR videos which have step by step guides. The issue with what you are trying to do is that you are trying to teach yourself. It is much easier with someone to show you how the first bunch of times and give you some pointers. At least that's how it worked for me.
There is no going back after you IV, unless you are one of the very, very few people who can try it once and not go back to it.
There is nothing glamorous about it, or cool. It is dangerous, often dirty, and risk filled.
If you must do this, I will give you the same advice that was given to me by the first person who taught me to do it.
Always use sterile water, or at least boiled then cooled water. But bacteriostatic sterile ampules are the best. Always use a fresh rig. Regrettably I must admit when I get desperate and only have one or two I'm prone to stabbing myself over and over with an increasingly blunt needle. However those incidents are few and far between. Always wash your hands prior to getting prepared. Have plenty of alcohol swabs on your person. Have an appropriate filter for what you are using. When preparing the shot, use alcohol swabs thoroughly on your hands before touching anything then before injecting swab the needle, your injection site, and the hand you are using to feel for a vein with seperate swabs. After you have injected, press a cotton ball (not an alcohol swabs, this increases bleeding) over the injection site and lift your arm up in the air. If you feel yourself start to miss your shot (you will feel a sharp sting when this happens and it will be painful) and you are not registering as being in the vein anymore, then discontinue the shot immediately and do not continue injecting. When you inject, don't just go fishing around for veins, make sure you register by pulling back on the syringe to check if you are in one. It will be very obvious when it happens. Practice using both hands equally so that you don't bash up one single vein, and rotate your injection sites. Be clean and hygienic, always. Try not to inject in public or anywhere you will be in a rush. Try to do it in a calm, non rushed environment.
Again, I urge you not to do this and at the very least if you look at my list of advice and don't think you can follow it I would suggest not going ahead with this, because that is the bare minimum you need to do in order to be as safe as possible.