I'm not an expert on the game (haven't even finished my first game yet!), but it helps if you have an interest in space and space rockets in real life to keep you motivated.

There are built in training scenarios to guide you through basic rocket construction, through to orbiting, landing on the mun (Kerbal equivalent of the moon) and ending with grappling an asteroid and redirecting it. I started with those training scenarios myself, so I would recommend doing the same.

It's a reasonably complex game so far, but it isn't necessary to grasp that complexity all at once. You will need to get comfortable with things like TWR (Thrust to Weight Ratio - if this ratio is less than 1, you won't have enough thrust to counter gravity so you wont move), or dV (Delta-V, basically the measure of the velocity gained by using up all the fuel for that stage) fairly early on.

It's a shame there isn't a demo to try (One that had all of the training scenarios would be ideal).