The first thing I would suggest is for you to answer some self analysis questions about yourself in MWLL.
- Which weapons are you good with?
- How good is your piloting? i.e. How well do you maneuver (legs and torso) to spread damage or protect a weakened component? Do you know how to dodge enemy fire such as LRMs, Arrows, MRM volleys, or even LBX alpha strikes from Fafnir's/Madcat Mk2s?
- Do you know when to retreat and when to pursue?
- Do you know the mech variants well enough that, upon sighting an enemy mech, you immediately know what variant it is and the best component to aim for to kill it efficiently?
Answering those questions truthfully you will see if you are a mechwarrior who is better suited to getting in close and brawling, hanging back and sniping, which mech you should be using based on what you know about the current battlefield situation (based on toughness, maneuverability, and weapon load out), and how you can best contribute to the overall strategy for your team at that time.
In more general terms, however, if you are looking to gain money quickly and efficiently then I cannot suggest more strongly that you should stick together with your teammates. Focus fire on enemy mechs and bring them down quickly so you expose yourself and your lancemates to less enemy fire. As long as you have done damage to a foe, if another teammate kills it, you will get a proportional amount of money for the kill as well, so there is really no reason not to focus fire and kill stealing is pretty much a null concept.
While sticking together with your lancemates, watch what they do, learn from them, and most importantly, talk to them. Coordinate your strategies and you will overcome an enemy that is functioning as a mob with no combined strategy. Example: Your lancemate gets a Catapult B (2 MRM-40s), if you get an Uziel E or a Raven Prime, you can then provide him with NARCs which will make those 2 MRM-40s perform 2 or 3 times better.
The other basic tactic is to simply cycle through enemy mechs and find the most damaged ones and finish them off. This is also true for mechs that have critically damaged components like arms or weapon pods. If you see that, it is low hanging fruit that can make a world of difference not only for you in the ensuing combat, but for your entire team. You will also get a nice little cash reward for destroying those weapons and take less return fire as well.
As for your choice of mechs, I think a lot of your trouble is in the fact that you are choosing mechs that utilize the AC10 (or UAC10). Currently this weapon is considered to be under performing by a significant portion of the community. I would suggest, instead, that you use pretty much any Bushwacker other than the Prime variant at this time.
As for the Warhammer, I would recommend against using the one with the 2 AC10s. Try the C, it carries a pair of LB10xs (making it really good against aircraft) and an MRM-20 (which does pretty decent damage as well). The slower reload time of these weapons means that you will have plenty of time to practice your piloting skills and torso twisting to spread damage and protect damaged components from enemy fire while your weapons reload. With just a little time in a Warhammer C, potentially with some aircraft kills, you should have enough cash (roughly 40-50k) to sell the Warhammer and purchase one of the Awesome variants.
I hope this helps.