Buying Pre-Formed Pipe Sleeves
One way is to measure diameter of your pipes and buy pre-formed pipe sleeves. At the time you buy the sleeves make sure they tightly fit the pipes, and that will depend on your measurement. Loose sleeves will not work effectively, so make sure you have the right measurement and sleeves fit the pipes. Also look for quality of sleeves and look for a better rated product, because it will provide all the needed and required care to water pipes.
Clean Pipes Before Putting Sleeves
It is possible that pipes have caught dust or even rust while they were left without insulation sleeves. So it is better to clean them with a soft cloth or brush before insulating them with the pre-formed sleeves. This will help in better fitting of the sleeves.
Follow Instructions Closely
It is most likely that the manufacturer's instructions are available along with the sleeves. So carefully read all those instructions and follow them by insulating the pipes. This can make your task a bit easier and you can get better results without much hassle. Also you can get some help about better measurement of your pipes etc.
Use Duct Tape
Do not forget to run a duct tape to a length of the slit in the pre-formed sleeves insulation, as otherwise your insulation will become ineffective in a shorter period.
If you are going to insulate your pipes with a fiberglass insulation use R-7 quality. This quality rating is recommended for an area with average weather conditions, but if your home is faced with severe weather conditions i.e. harsher cold, you can use an even better quality.
Again, you will need to duct tape the insulation to get better results. You can use duct tape also around joints or areas where insulation is less effective. Be careful and do not press hard the insulation, it will lose its effectiveness.