The key is to make sure you have a good brand of ecigs to begin with, or you will get too frustrated with battery life, always having to charge much more often, and carts running out only after 20 puffs or so.
There are so many good ones, so you may want to read the reviews to see which ones are the best (battery life, best carts, atty's, juice suppliers, etc..)
MY advice (although I'm a newbie so there is surely better advice then mine..lol) is:
-Get a bigger ecig that has a bigger battery volt. I have the Inferno by Volcanoecigs.com They come with a 650 mah, and a 1000 mah (both lasts up to 2 days after ONE full charge).
And the 650mah is also a passthrough USB (how great is that?)
-The bigger the ecig (length, size, etc), the more it will last--and most likely be able to withhold much more juice.
Although some do require constant dripping into atty's (if you are NOT using carts), then you might be using much more juice more quickly...just saying..
Although drip tips are very nice---but do be warned...dripping must be more constant.
-You're best bet is to order any ecigs from a company that has warrenty coverage--like Volcanoecigs. They have a 1 year warrenty...which is a good thing since I now Own TWO Inferno kits.
-Yes, as above, you may want to invest more then one kit---for any backups (incase one kit dies, gets ruined, or breaks for some reason)...you will then have another kit for backup.
-I buy 30ml ejuice, so because I'm not 100% vaping (yet--still trying to get fully off analogs), until then...I only use about3-5 drops of ejuice in my carts and I don't use them that often unless I'm vaping 0 nicotine in between real ciggs..(for now)..
-Buying blank carts and at least 2-4 bottles of 30ml (or more) from certain companies is the best way to go...since you can always refill, clean, and ejuice will last you.
Hope this helps some...