Hi @wgpubs
The values will be different for different models and tasks, you should try and see what works for you. Also, almost every pre-trained model comes with some default values which you find in its config file.
For ex, if you look at bart-large-cnn model’s config 2, it uses  4  num_beams with no_repeat_ngram_size  3.
Also, this blog explains different generation arguments and should help pick values for those https://huggingface.co/blog/how-to-generate