Strictly speaking, the rules say you cannot call your first serve out. However, the rules also say you should also call your own balls out if it is obvious.
The "big picture" is that USTA does not want servers call their own serves out in cases where the return is a "winner", because that is an advantage to the server, for being "honest". Being "honest" should never work in your favor. You may lose points over honesty, but no player will go home feeling bitter about being cheated.
If you hit a serve you think was out and dont/cant play the return of serve, ask your opponents what the call was. If they say "yes", then forfeit the point. If they say "no", take a second serve.
If you hit a serve you think was out and your opponents do not call it out, proceed to take a second serve. If your opponents ask you what you are doing, tell them your first serve was out. If they disagree and say your ball was in, then take the point. If they dont object to you calling your serve out, continue with second serve.
The only time i've been argued with over calling my first serve out was when I beaned an opponent with my errant serve. Basically, kick serve + sun = equals frame. After my opponents insisted I take the point and brief friendly banter-laced argument ensued (because, there are actually no rules that supported my position. I cannot call my serve out; I hit an opponent with the serve, therefore we win the point) I agreed to take the point. This is a much better situation to have than your typical argument over calls.