Many people want to start playing Dungeons & Dragons, but they only have two or three friends to play with. While almost all adventures, modules, and campaigns are written for larger groups, it is actually a lot of fun playing with a smaller group as the game is more focused. In my experience, adjusting existing adventures to a smaller party size often does not work well. The difference between a large and a small group is not only sheer combat power but also versatility. Most larger groups have at least one fighter, one spell-caster, and one healer, which guarantees some level of resilience.
I therefore believe it is necessary to write adventures especially designed for 2 or 3 players. I used a number of mechanisms toward this end. First of all, there are NPCs that can accompany and support the PCs. As there are multiple options, the DM (and the players) can choose which ones best fit the group configuration. Also, having multiple NPC friends is more fun; they come and go, and we also enjoy meeting an old friend after a while, don't we?
Magic items can help with the problem. Healing potions can make up for missing healing skills, for example. Some items allow you to summon creatures, which is great for balancing battles.
Finally, allowing different solution strategies for conflicts accommodates groups with more specialized skillsets. Stealth, diplomacy, or magic are sometimes great alternatives to battle.
So that's all! I hope that Bugbear Awakening (the only adventure I have written so far) is fun to play with your small party of adventurers. I am always open for suggestions on how to make it even better!