I’m not experienced enough as a modeller to offer very much advice. For that reason I am very happy to refer you to an excellent site that offers lots of useful advice for the beginner – The Model Makers Resource.
The author presents a range of valuable hints and tips. Perhaps one that frustrates most newcomers is the problem faced when applying acrylic paints to a plastic model. Here’s an excellent piece of advice:

Before you begin painting you also need to make sure that the model is perfectly clean. Dust, oil from your skin and residues left over from the moulding process will all serve to make a hash of your finish. Metal parts can be cleaned with alcohol while good old warm soapy water is the best all rounder. Be sure to rinse off all the soap before you tackle the problem of drying it!

And with that useful “taster”, check-out the other articles which for convenience I have listed the main links below:

• Photoetching at home
• How to Paint
• Working With Vinyl Parts and Kits
• Working With Resin
• Working With Brass
• Mould Making With Latex
• Working With Vacuum-Formed Parts and Kits
• Useful Geometric Techniques
• Working With Polystyrene Parts and Kits
• Working With Clear Polystyrene Parts and Kits
• Applying Decals
• How to Solder
• Marking Panel Lines
• Landscape Modelling
• Making Model Trees
• Modelling Water
• Working With Plaster
• Using Bare-Metal Foil
• Understanding Scales
• Architectural Model Making