1.) Mini Marshmallows: This one may be obvious, but use the mini marshmallows. They melt faster and much more evenly than the big ones.
2.) Name Brand: I am generally not a name brand kind of girl. I go generic all the way. But I admit if you want the best results, Kraft marshmallows have the best melting capacity and Kellog's Rice Krispies have the best texture. If you are making these for your 5 and 7 year old though, go generic. They won't know the difference. (This is totally an unbiased opinion, I'm not sponsored by either of these brands.... yet... I'm looking at you Kraft. Ahem.)
3.) Cook marshmallows low and slow: Everyone has the tendency to speed through the melting process. But the mallows need some serious love, people. If you try and rush through this, they will get hard once they cool instead of keeping the chewy texture everyone loves. So to avoid this, turn that heat down to low. It might take a bit longer but it's worth it!
4.) Save some marshmallows until the last minute of melting: Save like 1 cup of the mallows until the last minute of melting. That way you get a few chunks of pure marshmallowy goodness.
5.) Heaping: All my recipes use a 1:1 ratio of marshmallows to rice krispies. But I must admit that my measurements are usually heaping when it comes to marshmallows. (So when I say 6 cups of marshmallows, I mean 6 generous cups... no skimping)
6.) Add vanilla: It's amazing what that little bit of extra flavoring can do. Trust me.
7.) Add extras during last minute of melting the marshmallows: You want to add all the flavor enhancers (i.e. cake mixes, pudding mixes, etc) before the marshmallows fully melt. My advice is to add them during the last minute of melting the marshmallows so all the sugar crystals have time to dissolve. (Nobody likes grainy mallows!)
8.) Let the rice krispies sit 5 min before pressing into the pan: Simply dump the rice krispies into the pan and let them sit a minute. This helps avoid a soggy or stale texture. After a minute or two of cooling you can then press them into the pan.
9.) Use a smaller pan. In most all my recipes I say to use a 9x9 pan because I like my rice krispies nice and thick. Realistically you could use a 9x13, they will just be thinner.
10.) When in doubt, add more marshmallows :)