Ok well from my experience, and that being:
350gt at 19 with 1y ncb insurance was £1290
Crashed that jan 2015
Got another and insured it when i was and am 21 for £1200 with crash declared and a few mods declared too, i am currently with bell and was last time, they give you a box for the first three months that you plug into your cig lighter and its powered from there, simple and got me a £50 discount this year and 80 last time. The next closest prices the first year without a box was about 300 more and the second time about 200 more so up to you whether u put up with a box or not for just 3 months
So what i do is i go on comparison sites like go compare and compare the market. I then do all the usual, your details, your cars details, if your young put an experienced driver with no crash history, you dont even need to be related, as a second driver. Preferably someone where the job can be called 'office worker' (cheapest job for insurance quotes) and then dont include any of the mods on your car, leave tht as no mods. Then when you get to the results where the different companies prices are, go onto the cheapest or the one you like the most and go through it until you end up on their site which will give w summary of the details of your cover, i then added the mods at this point (if i added it originally a lot of companies wouldnt come up at all) then finish editing the bits for your car and see the final price. if anyone has any specific queries about what else i put to get lower insurance feel free to message me im new to the forum but am on the skyline owners forum due to them having a 350gt section (the car i own)