Very American, but Steve Good has his followers:
http://scrollsawworkshop.blogspot.com/In terms of practice patterns, just google clipart and go from those pictures. There are also quite a few free patterns on the web if you do not mind what you make and just want cutting experience. Lettering using MS Word or PowerPoint is also good practice. Jigsaw patterns can also be a source of good practice patterns for flowing but small turns.
You are looking to cut some very fine lettering from your image and it will take time to be able to do this reliably. The hardest part will be to get a smooth flow to your lines. For the beginner, this is usually because they try to adjust too quickly the line of the cut i.e. the blade starts to drift off line and there is an immediate reaction to get back on the line as quickly as possible. If you can drift back to the line instead it will avoid the jaggedness that can result from sharp deviations.
The other thing that will take practice is sharp turns or corners. When these are internal you can come at them from both sides to make the 'point' sharp. When they are external, it is far better to do a loop, going past the point into the scrap, turning a full circle and then coming at the other side of the point from the opposite direction.
As with anything - practice makes perfect, and it can take a lot of practice to be good. Don't be disheartened if your first attempts are not exactly as you would want - it can take a while to get into the groove with a scroll saw and I find it is one of those things that I have to do constantly to remain good at it.
final thing - blades are key. Get the right size and tooth pattern for what you are wanting to cut and don't be afraid to replace them often. I use Flying Dutchman blades from the US. Although I haven't tried then, Pegasus blades are now sold by Axminster I believe and seem to get good reviews. You will not be able to get decent blades in a DIY shed such as B&Q etc.
If you do not get a good edge, or get feathering on your cardboard, either sandwich it between two other pieces of card and take the middle one for your work; or if it is going under leather and does not matter wrap the card in sellotape front and back. This will also help lubricate the blade and will hopefully give you a smoother cut.
Failing all that, sell the Hegner and get a laser cutter