If you have the resources, salvage in the field is cheaper then salvaging the Mechs after the mission is over. Any Mech you salvage in the mission with the salvage craft, you keep with the rest of your Mechs in recovery. It only costs 10,000 resource points in the mission to salvage a Mech, while after the mission in the salvage screen it can cost from 20,000 to over 150,000 resource points for salvage. However, only do this with Mechs that are worth salvaging. If you have any resources remaining after all the objectives are complete or the enemy destroyed (whichever comes first), salvage whatever Mechs you can and sell the useless ones when you get back to the screen.
The best Mechs to use (once they are available) are as follows:
Cyclops: Has the best sensor range of any Mech as well as an impressive weapons load. The best mech in a group.
Men Shen: Preferably used in the near beginning of the game as a sensor and recon Mech. Probably the heaviest mech with ECM suits.
Razorback: Use these at the beginning of the game as sensor mechs until the Men Shen is available.
Shadowcat: Good fire support and escort Mech for larger Mechs. It is the lightest mech in the game other then the Hollander to be equipped with the a Gauss Rifle as a standard weapon. Its advantage over the Hollander is that it has more weapons for shorter range combat, while the Hollander just has the Gauss Rifle and can easily be disarmed.
Thor: Has a good weapons load for short, medium, and long range combat.
Vulture: Good choice as a missile Mech, second to the Mad Cat.
Post your Mechs on guard mode on top of hills. They can see the enemy coming earlier then normal and have a distance advantage. Also, any weapons fired will come down on top of the enemy (which is dangerous for Mechs because their head cannot take a lot of the damage, which means the pilot could be killed). With that in mind, do not put yourself in the low valley position, unless you are sure there are no surprises on the hilltops ahead. The one advantage of being down in the hills and valleys is that you can evade enemy radar at the same level as you.
Mix light and heavy Mechs in your groups. Have a couple of heavy Mechs in the group, then set the lighter Mechs to guard the heavier Mechs, then just select the heavy Mechs to control. With this you can control certain Mechs while others which are set in guard mode will attack the enemy automatically without orders. This is useful for base assaults. While your lighter Mechs keep the enemy busy, you can take your larger Mechs and destroy your main objective or hit the enemies hard from behind. Keep in mind that in guard mode the Mechs often swarm and circle the enemy and hit it from all angles. Again, set the lighter or faster Mechs to guard the larger or slower Mechs. Deselect the Mechs in guard mode, then select the heavier or slower Mechs and control those only. The Mechs in guard mode will do everything, from attack to evade, automatically.
Gas and fuel tanks:
Gas and fuel tank explosions are one of the most dangerous accidents in the game, but also the deadliest weapons. It is a good idea to lure enemy Mechs into range of fuel tanks and blow up the tanks, thus taking the enemy out. However, the enemy will also do the same thing to you.
All Mechs have a primary configuration. However, all these configurations are set with weapons to have an advantage at a certain range. Its a good idea if you have leftover resources after you buy and sell Mechs, etc., to customize and play with different configurations set with weapons for all ranges of combat. The Mechs will not fire long range weapons at short range. You cannot set one Mech with long range weapons and expect them to fire from long to short range. If you do this and the enemy has shorter ranger weapons and is faster, it can easily run within the range of your weapons and take you out. Long Tom cannons and Swarm LRM racks focus devastation on a wide range effect area rather then a focused point. Make sure your allies are not near an enemy when these long range weapons are fired. Also with Mechs, when they are completely destroyed, their nuclear reactors explode. However, unlike the original Mech Commander, the explosions can hurt you. Any of your troops near a Mech when its reactor blows will get damaged, or if they are right on top of the wreckage of the exploding Mech, they could be killed on the spot. This is what makes close range combat deadly. Most Mechs usually move away or move to the next target before the enemy Mech explodes. Immediately move those that just sit there.
When repairing damaged Mechs and vehicles, keep in mind that there is a limited amount of repair resources. When you repair, make sure you make them responsibly. Do not repair all your slightly damaged Mechs, use up all the repair resources, then try and repair your heavily damaged Mech. This applies for all repair systems: the Repair Truck and the Mech Repair Bays. Note that vehicles can only be repaired by Repair Trucks, and cannot be repaired in Mech Repair Bays. Mechs can be repaired with either source.
Repair while walking:
If a jump-capable Mech is damaged and you have a Repair Bay captured, select the Mech to jump to any location. While in the air, select the Mech to repair in the Repair Bay. The Mech will land, then start walking to the Repair Bay. Do not order the Mech at this time. While walking, the Mech should be repairing. Note: If the Repair Bay is in a base, you must have the Gate Control under your command or the Mech pilot will tell you he or she cannot get there.