First, most Spanish speakers do not have a difference between /b/ and /v/. It's like saying that you can distinguish a Bostonian's /s/ and "soft c" or his /k/ and "hard c."
The two sounds merged for nearly all Spanish dialects over a century ago, and longer ago for some. Just like <z> and <s> merged (/ / = sound, < > = letter).
Second, Spanish subjunctive is very much not the English subjunctive. It's used (in Spanish) in all sorts of places where it's not used (and possibly has never been used) in English. And, formerly and formally, we use it in English in some places where it sounds bad in Spanish.
Third, two things really matter for learning to speak.
The first thing is inhibition. Kids learn to speak and make lots of mistakes as they figure things out. They have no inhibitions. The old advice to have a shot of whiskey is actually one to "lower your inhibitions." Don't worry about making mistakes. Most of us have a little voice that monitors what we're saying when we're anxious or self-conscious. Turn it off (easier said than done). Most Americans are inhibited because we somehow feel silly speaking a language that we don't see a need for and have seldom heard.
That "monitor" thingy is obnoxious. Kids don't have it. It can help train us in the language faster than kids learn language, but it needs to be controled. Otherwise it helps with slow speech but ultimately sabotages any attempt at fluency.
The second thing is how badly you want to speak, your motivation. It's easier to learn to speak in an immersion class because English isn't an option. If you want to speak you find a way. You puzzle out how to explain how you're related to your mother's cousin's sister's husband if you feel you have a need to do so--you sort through the words you have, the grammar, and voila--there's your sentence. If you need to go to the bathroom and the teacher refuses to acknowledge, "I need to go to the bathroom" you will find a way. Wanting to somehow "be like" the speakers of the target language also matters. If somebody looks down on Germans as Jew killers they're not likely to much care about German culture or want to "be like" Germans. If you think of them as the bearers of the culture of Bach and Goethe and Grass then, well, there's a motivation for learning the language. Most Americans simply don't see a need for a foreign language and we feel that English is always the better choice. (This separates out the serious learners from those who want to "be in solidarity" in some obscure, abstract sense of the word.)
The problem is getting inhibitions lowered and motivation up in time to practice over the next 4-5 days. In Russian class we were told to read something or produce a vocabulary list, get a stopwatch and then talk to the wall on that topic for so many minutes a day. The wall isn't going to embarrass you, your monitor will shut up, and your mouth (and brain) gets the practice. We were also told to find things that we thought mattered, but this was in a more advanced class--early stages you're stuck with "Please, Mr. Gonzalez, where is the bathroom?" and "My name is Jean-Pavel Yitzhak bin Rahim, I have a reservation."
It was the same with writing. We had to write a lot--just practice. Some things were graded in gory detail and we were to re-write them until we had no mistakes; others just got a check. Either way, there was no downside--we practice and that's it, or we practice and we're told what to fix, no penalty. On rare occasion the initial draft was graded, sometimes we were warned sometimes we weren't. The point: Our little monitor voice shut off for that, too. We blathered on paper and got over our collective writer's block.
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