For years, I couldn't make a barre chord, and learned to use my thumb on the bottom string to make that nasty "F" chord. I still prefer this method, for a number of reasons including what McGrath said. It's just easier to change chords, work in bass runs, and pick off-chord melody/grace notes (especially in the key of C, which is when I use the F chord most often, anyway).

I still prefer to wrap the thumb around for F and other similar chords up the neck, i.e., all those that are shaped like an "E" just below the barre (F#/G/Ab/A/etc.). On the other hand, I eventually found it easiest to use the barre configuration for the bB and BbMinor forms (chords shaped like an "A" or "Am" below the barre). Depending upon the sequence and speed of chord changes, I might stay with the barre for a quick "F" (or variation) when also playing barre chords of the Bb family.

Another nifty trick I learned and have adopted -- when in the key of G, you can play your D or D7 chords by sliding a C or C7 two frets up the neck. You can mute or avoid the top sting (when playing the 7th, you have to), or else fret the top string with your pinky on the "third" fret (that is, where the third threat would be in first position when playing the C chord.) The open "G" string is not, strictly speaking, part of the D chord, but it's fairly harmless to let it sound without muting it, since it's the tonic note of the key you're in -- the "drone" effect is similar to what a 5-string banjo produces on a D chord in the key of G.

Yet another hint especially applicable to the key of G, but also helpful in C and other keys -- instead of making the G chord with index and middle fingers on the bottom two strings and ring finger on the top (high E) string (as usually taught to beginners) , use the middle and ring fingers on the two low strings and your pinky on the high string. Assuming you can use your left pinky at all (I know that may take a while), it is MUCH easier to switch back and forth between this configuration of G and C, and also to include the "two-frets-up" D chord described above. Also easier to move back and forth between G major and G7 and, in key of C, to move among C/F/G/G7/Am/etc.

Regardless of the chord "shapes" you adopt, a good beginning-player's strategy is to learn a few simple bass-note patterns to "walk" the bass from one chord to the next, between your full-chord strums. It's pretty simple, and can add a lot of interest (and an impressive, seemingly complex flavor) to your accompaniment.

Within the next year or so, before you learn any really complex picking, you can start fingerpicking with a simple, memorized, four-beats-to-the-measure picking pattern that you can use for virtually any non-waltz-time song. Next, insert your walking-bass tricks into the fingerpicking pattern. To the casual listener (everyone except us fellow players), you'll be as accomplished as anyone by that point.