Not hard. Buy an Estes kit. Go along to one of the regional meetings, fly your rocket and talk to people there - they are very friendly.

The UK regulations are fairly sensible and they won't let you do anything stupid at one the regional meets. Just start with something small (A/B/C motor) and work your way up from there. Don't try to start with a K motor, 2 stage or liquid propellant and you'll be fine.

Where are you based?