Advice

1. dont use peices that arent in the style of your convert e.g i got a converted destroyer off ebay with 2 guass cannons (nice) and 2 chaos chainswords with the hands still attatched (no)
2. green stuff is good for securing awkward joints
3. plan ahead, dont start till u hav at least a vague idea of how your finished model will look like
4. keep in mind the material your working with, metal bends but snaps, plastic only bends if melted but is easy to cut and glue

Tip for plasticard, when bending, bend into desired position then aim hairdryer at it and keep heating it until it doesn't ping back

Tip for clipping to rotate arms - ensure you have spare hands. The amount of hands you'll find by searching the corners of my room...

b4 building big models, think long and hard about how u want the finished thing to look
research what each wargear does
only then build the model

I agree whole heartedly with the previous post.. If your making a model that was once in epic, try getting a model of it so you can see what it would look like in 3d-- like the Imperiator in Manc GW!