Hang in there! Falkow can be discouraging at times, but in other games you almost feel sorry for opposing spheres. I'm up to level 20 and haven't settled on any one particular strategy. One might be able to get a better record with a finely tuned cardfile and disciplined play, but I'm having more fun throwing new files together and seeing what happens. General tips on cardfile construction: plan your first 2-3 moves, even to the point of mapping them out once you know which sphere your opponent is playing. If a standard opening like kurina/combat monk or leonardo/shade is going to destroy your setup completely, you probably want some way to adjust mid-game. Plan your first couple Soul Card activations too. After that, look for 2-4 more cards with some synergy for the meat of your deck. An Azure Beastmaster to help out your Sea Hunter, or a pinpoint duo like Scythe Soldier + Swallow Scout with some help from one of my favorites:Wizard Soldier Apprentice. A word on him: he works especially well with Falkow whose agi advantage typically means you can use the ATK boost to take out threats before they have a chance to attack. Park last turn's Sylph next to him and you have a 3 agi attacker dealing 20 damage.
Another nice Set 2 card to play around with is the Invisibility Edge (+10 ATK, +1 RNG). The range boost lets you park someone like Eagle Soldier behind the front lines (and still deal damage if you don't want to spend the SP), either as a middle-row blocker for your way-back or just somewhere out of the way of your opponent's front row. It can be used to boost the range of a special ability like Wind Sorceress Femiel's -20 HP to all in range Berserk Wind. In general though, use it to bump damage of key units up: a Haste Soldier doing 30 damage can keep Kurina knocked out without a chance to retaliate. Since it is a grimoire, it takes effect when revealed, meaning you can get a jump on your opponent, maybe 1-shotting a blocker they expected to survive at least 2. In the best case scenario, this kicks off a domino effect, with your other units taking full advantage of an opening, for just 1 SP and one card selection!
If a cardfile isn't working out, it might be your Soul Cards. Are you getting field buffs on an empty field? Row damage that hits a single, high-def damage soaker? Wishing you had just 1-2 more SP over and over? By tweaking your SC lineup and activation strategy you can boost a cardfile considerably. For example, if you want to buff your field, try using Undine one turn, then placing her in the front row in the following turn. There's a good chance she'll get hit randomly, giving you the option of letting her die for the LP hit and subsequent SC activation. Take a look at what your opponents are playing, and see if that gives you any ideas (besides spending $200 on packs...) If you've got an Assassin, I'd highly recommend putting it in your SC lineup somewhere. Sending a big baddie to the Cemetery along with a liability like your last Undine can really help your game.
While you're still learning, take the focus off your winning percentage. "You Win!" might be a nice little self-esteem boost, but if you let the losses drag you down just as much it'll be a tough road. Go in with goals like "I'm going to try to get these 3 cards out together" or "Let me see how this opening works" and you can be successful even in a loss. Even spectacular failures can be entertaining. Good luck!