flat betting is a great strategy, especially when starting out. And by no means do I mean only amateurs flat bet. I flat bet on the vast majority of my wagers, when I wager at higher levels it is usually on some sort of subset that I determine (ex. playoffs, or strong angle that historically produces +60% winners).
The advantages of flat betting IMO (feel free to add or subtract from this):
1. it keeps one from losing big on the "lock" strategy- the fallacy that there is virtually NO WAY a given team can lose the event. Probably the biggest pitfall for bettors is putting a huge chunk of BR on ONE event only to be on the wrong side of a "fix" Boxers like Klitschko lose, as do pitchers like Pedro. I have come across many "professional grade" gamblers that think it is very foolish to flat bet- most of these same people all too often try to explain why this line they determined was 10 points off didnt cash. Whenever I find a spread that seems to be way off (CHI o/u 12) I try very hard to find the data that leads the bookmaker to this conclusion. If I cant reasonably determine what I might have missed, I usually watch line movements VERY closely. If the flow of money doesnt change the line, then usually that is a good indicator of how solid the book maker feels his opinion is on a line (esp. on home dogs). It is generally a bad idea to bet against what I call "bookmaker opinion" over time, and if you are wagering a large chunk of BR on these "locks"...
2. Flat betting helps keep things simple. I have been pissed off at myself plenty of times for going 3-1 and LOSING money. Continuously stressing over the 3X BIG play each day in order to make money sidetracks a lot of people from what the goal should be- spotting enough value to win +52.4% of the time. If each wager is the same size, then one must only spot events that have a 55% chance of winning to do fine (sounds a little too simple...). If you feel that you have enough experience to vary wager size, set parameters for those types of wagers. A great starting point could be a home conference in NCAA sports where you could have more time and info access than the bookmaker and have a bit more of an edge. Write down something like- I have decided to wager 1% on NCAA basketball games, but 2% on Big Sky inter-conference games because last year I won 59% of those bets. All too often those double bets will stray to random top 10 teams (on the road), and that will usually take away from the edge you are trying to establish. Keeping accurate records is really the only way to see what kind of edge, if any, that you have over the house, and it is a LOT harder to go broke when you are flat betting at a low percentage of BR WHILE you are tracking how those BIG wagers would have done over time.
Stay away from parlays. Just stay away. The worst thing that can happen to someone starting out is winning a couple of parlays. Nothing builds that invincible feeling more than the winning parlay. Ever see the Hilton NFL Parlay Contest? Ever see anyone anywhere post only parlays? nope. Not only will you pay more juice on them (except 3teamers), but you will PROFIT MORE by playing each play straight up, over time. And worst of all is playing a few games, and then parlaying all of them together on top of the straight wagers...I do play a few parlays, but almost the only time that I play them is when I can reasonably determine that one outcome is correlated to another- same game side and total. I generally play this parlay when I am worried that if I played the side straight up and the total straight up that if the other team scored just x amount of points it could very easily cause both bets to lose, these are few and far between.