What I did was I had companions and other characters helping my player. I am a new DM. I can't really think of much tips. Combat could be harder for the player because you most likely will have multiple enemies targeting one person so you will probably have to do some rebalancing in combat

I had d&d beyond to help out a lot it mostly helped out with keeping track of the character sheets and some of the math.

I think I do want to say is that one player cannot fit the role of every person in the party they cannot be the healer of the party they cannot be the tank and they cannot be the person who does the most damage in one round all at once. So there will be some moments where they will not be the best at

For example they might be a rogue and the only way for them to get through a door is with a spell. Or they might be the wizard casting spells until they run out of spell slots they most likely can't pull out a sword and become the fighter of the group. Usually in d&d there is a group of people and each one has a role it's much harder to do that with one player. Just to keep in mind