Electric heat gun whenever possible.
Soldering iron tip, Bic lighter or other as needed.....
I got my heat gun at Harbor Freight. Less than 15 bucks and works great for heat shrink.
Works great ...and goes as low as $12 when they have a sale.
I would be careful using a lighter. I have been working Avionics int the USAF for 30 year. I have seen to many time when a light is used the heat shrink gets over heated and becomes brittle.