Well yes, yr dsn should have given you some rough guidance but failing that, the best way is probably to keep to eating a std amount of carb for each meal like 30g and then bg test every 2.5hrs and try to figure out an amount of bolus to keep bg levels at safe levels according to NICE bg guidelines. A good target is something like 6mmol before eating a meal and then 2.5hrs later allow for a rise of about 8.5mmol which will then drop back to about 5 to 6mmol 2hrs later within the 4-5hr acting time of the bolus. Most people start with a ratio of 1u to 10g carb and then adjust the ratio to keep within the NICE guidelines. So, start testing bg levels and then start to find your way with finding the correct ratio to use. There is good online guidance using the BDEC carb counting course. That's how I found my way with using bolus/basal insulin safely.
Hope that helps you a bit....good luck