How do you get Ho-oh in Pokemon Silver?

Answer 1

First, beat the Elite4 and Lance.

Once you reach Kanto, you have to get to Pewter City, which means you'll have to beat most of the gyms in this region (because the storyline pretty much forces you to do it in order to be able to reach the first cities, like pallet town).

Once you reach Pewter city, there should be an old man near the pokemart. Talk to him and he should give you the Rainbow Wing.

With the Rainbow Wing in your inventory, go back to Johto (fly to Indigo Plateau, then to New Bark town, or simply get the Magnet Train Pass and go on the train).

Go to Ecruteak and go to the Bell Tower (same place where you battle Suicune in Pokemon Crystal). Once you're in there, you must reach the top of the tower. Once you do, you should find Ho-oh waiting for you there.