Recently, I posted about adding sealant to my tubes to help eliminate flats (How I Eliminated Flat Tires Forever Part 3). However, adding sealant to a presta valve tube is easier said than done, especially, if the sealant uses particles to seal the puncture like Slime sealant. Consequently, I would recommend that the easiest and probably the least expensive solution is to simply purchase self-sealing tubes with the sealant already inside.
However, if you are a do-it-yourselfer like me then I would recommend using tubes with removable valve cores. The cores can easily be removed and the sealant injected directly into the tube, saving you a lot of time and headaches. Nevertheless, if you are on a tight budget and need to use your existing tubes without removable cores, the next best approach is to put a small hole in the tube, inject the sealant directly in the tube then patch the hole in the tube.
Finally, don’t added more sealant than necessary. For example, although an 8 oz. tube of slime bicycle sealant says that it is enough for two bicycle tubes, in reality that is overkill. Adding 4oz. of slime to each tube is probably unnecessary and just adding weight to the tube without improving flat protection. Check the slime calculator to find the optimal amount of sealant necessary.