Salvage a "Clan Targeting Computer" and equip it on your mech. Then target a mech's head and fire a large pulse for a one hit head shot kill.
Blow the legs off a mech, rather then the torso. Or, better yet, use a head shot.
Put your ammunition on the arms when you build a mech. Normally, when your arm gets blown off, the items in it are also gone. However, this is not the case for ammunition.
Select the chassis Daishi. Un-quip everything (including Double Heat Sinks, etc.). Put 1 Er Laser (L) Clan in the head, 2 Er Laser (L) Clan in the center torso, 9 Er Laser (L) Clan and 1 Er Laser (M) Clan in the left torso, 2 Heavy laser (M) Clan and 1 Laser (S) in the right torso, 2 jump jets in each leg, and in the right/left arm you can put anything (ammunition, equipment, etc.). If you stay in the water on The Road to Madre, you will not be shut down as easily from heat.