One of the larger mistakes I see (other than anxiety, fear, and just plain old beginner's clumsiness - which everyone has in the beginning, heh, -) is this really ridiculous notion that fast results are equivellant to the best results.
Now, don't get me wrong...if you're anxious to have what you want (anxiety is still a famous spell-killer, and slower-of-manifestation, so that alone is a problem,) like most people, you will be "chomping at the bit" to get what you want. That means really getting crazy to get what you want and quickly for the idiom-impaired. ;) While I do believe most of us can understand your sense of urgency, the problem is, usually, the urgency for the manifestation is not at all a reality except in your own mind.
If it's regarding an impending bill, a job interview, stopping attacks from an enemy, or a court case...well, then time may very well be of the essence. However I see this a lot with love, especially reconciliation. :P
You don't *NEED* your ex back tomorrow. And for some reason, people seem to take this "bring back my ex now" as a life or death thing. If it's not happening now, it's not happening ever, - or so their panicked and unsettled mind tells them so, despite that not really being the case.
You need to remember that if the problem is one of complexity (such as a break up,) it very well might require some time to return to the state of romantic bliss, especially if the problems which caused the seperation and break up were complicated, and took a long time to build up. It's far easier to forgive a one time instance of certain transgressions than it is to forgive someone for 2 years of feeling pushed and pressured and bossed. And if the "singular" transgression is bad enough (for example, you slept with your boyfriend's brother, and also his best friend,) then it's going to most-likely take a LOT of work to fix that mistake.
If you truly believe a horrific break up with lots of hurt is getting fixed in under 2 weeks, using only one spell, you're probably fooling yourself. Even if it does get back together, there is a much higher chance of instability of the manifestation. I had gone over this in my QYAM post where I discussed using St Expedite for love, but it would seem I've got a good deal of confuzzled people emailing me, acting as if they don't get the ex they chased down the street with an axe back with them by next week, their spell is "fake" or "not working." Nothing could be farther from the truth. The culprit for that spell not working is easy to find. Stand in front of a mirror. Look who's looking back at you - it's you! - and that's who's the cause of the spell failing if you think you'll get your ex back in a week, and get angry when you don't.
I've gone over it enough times in here that everyone else is bored of hearing it. ;)
Fast manifestion does not equal the strongest or best manifestation. Just like a severe illness, it might require a lengthy treatment to "cure" the problem. If all you want is a fast manifestation, there is a stronger chance that your own impatience will be you and your spell's undoing.