When it comes to live shots, there's no easy way to slowly break in. You can't do part of a live shot, then work your way up to a full live shot.
But with anchoring, there's a way to slowly dip your toe into the waters.
This is an old method that worked very well years ago. Why News Directors don't do this anymore is beyond me. Some have an aversion to anything from the "old days." But this is how I, and many others of my generation, broke in on the anchor desk.
Years ago reporters took turns doing the morning cut-ins for a week at a time. Once every six weeks or so you'd see yourself on the schedule for cut-in duty. This served two purposes. It gave the morning anchor a break, and let reporters have a taste of anchoring. By the time you did four cut-ins per day for five days, you were comfortable with the set, the prompter, and how things work in the studio.
The best part of doing cut-ins is that they're so short. You read a quick story or two, toss to the weather person, then maybe read a tease for the evening newscast. All together you might have sixty seconds of copy. Not too much to get stressed over.
Compare that with a maiden voyage on the anchor desk doing a full newscast. All sorts of disasters can happen in thirty minutes, and the size of the script can make you break out in hives. It's too much, all at once. The other problem with breaking in on a full newscast is the snowball effect; once a rookie makes a mistake, the newscast becomes a snowball rolling downhill, with errors piling up on themselves.
If you're doing a sixty second cut-in, how bad can it be?
Trust me, this works. If you wanna break in on the anchor desk, ask your ND if you can do it in this manner. It's easier on you, easier on the viewers, and you'll develop a comfort factor that will make your first real newscast a lot easier. Your ND will develop a comfort factor as well, and he's more likely to "risk" letting you do cut-ins than a whole newscast. Nothing makes a ND break out in hives like throwing a rookie on the set for a main newscast and hoping everything doesn't crash and burn.
The deep end of the pool is no place for a rookie anchor. Wade in slowly if you can.