Singing on television is not an easy job. You can sometimes be lead to believe it is easy since some people make it look easy, but if you are a newcomer you could really do with some good advice from somebody who knows.
At this very moment, I am thinking of Clarissa and Josh in the Finnish final this year. This is what their performance looked like in the second heat:
Clarissa feat Josh - Top Of The World
Perhaps I would have a few objections to their styling - particularly that hood covering Josh's head for far too long - but that is less important here. Easy to fix, a light makeover could take care of that. There are much bigger problems here.
It is hard to sing and dance at the same time. Clarissa is moving quite a lot on stage - especially before Josh comes in - and it clearly affects her vocal abilities. Better to stand still and let the camera-work create the movement instead.
There must be chemistry. If you sing a duet, the audience wants to believe you have something going on between you. Standing very far apart throughout the entire performance is not a good way of achieving this.
It also looks ugly. The cameras can never catch both of you in the same frame without using a very wide shot of the entire stage. For television viewers, you will look like strangers dancing on your own. It takes two minutes before we get the first image of Clarissa and Josh standing together and it is a very short one. Too little, too late.
You must always be aware when the camera is on you. At 2:28, Clarissa gets a close-up at the same time as she starts jumping up and down, seemingly spontaneously. Had she instead sung straight at the camera, she would reach out much better to the viewers at home.
When you are singing at a concert it is important to focus on the people seated in front of you and try to convince them of your greatness. When you sing on television, it is so much more important to focus on the cameras. You sing for the people at home - the people in the hall are a special effect and not your prime target.
If Clarissa and Josh make it to the final - which I hope and think they will - I hope they will throw their present stage presentation out the window and start over from scratch. Find a choreographer who understands television, cut down on the dancing, stay closer to each other - so that the cameras can deliver many tight and pretty shots of the two of you together - and make sure you are always aware of where the cameras are. You don't have to look into them all the time, but you must be aware of them.
Eurovision is above all a television show. Design your performance for television and you will be fine. (Ignore the cameras and you lose.)