Of course smaller ensembles do not require a conductor per se, but someone to lead the rehearsals. When directing larger ensembles, I agree with Kev that baton technique becomes important for a number of reasons. I was trained in the school of minimalism where "less is more". In my experience, groups watch much more closely when the baton strokes are small and nuanced, rather than big sweeping and flapping movements which may provide some comic relief to the audience, but are musically quite unnecessary. In this style, loud playing requires a larger pattern, and soft playing a smaller one, but the pattern rarely exceeds the width of the conductor's shoulders. Please, please don't bend down to get the group to play soft. It looks like you are about to "moon" the audience. 🙂
I was taught to keep the baton at the conductor's eye level at all times. You see lots of directors conducting their belly button with the baton well below the top of the music stand well out of sight of the players. The left hand should be used sparingly to add emphasis. If used too much, it completely looses its effectiveness. Facial expressions such as smiles, frowns, raised eyebrows, grimaces, etc. can communicate a lot non verbally. If a player makes a wrong note, a glance and a grimace let's them know you heard it, and a smile afterward means, "it's ok, you'll get it next time". A smile and a nod right after a well played solo in a piece means more to the player than all the verbal praise in the world afterward.
It is important to maintain eye contact with the group at all times. Almost all inexperienced conductors bury their head in the score way too much at first. That's why it is important to know the score inside and out. When I was a student teacher, my mentor told the students in the band to silently scoot their chairs forward every time I kept my head down looking at the score while I was conducting. By the end of the song, the entire band had moved several feet and the flute section was practically in my lap, and I didn't have a clue. My teacher got his point across and we all had a good laugh.
The best advice I could give is to get a full length mirror and some scores of pieces on recordings. Conduct the piece as it is being played, giving cues, cutoffs, accents, dynamics, facial expressions, etc. watching yourself in a mirror. Another variation of this is to videotape yourself conducting the recording. It is really scary at first, but that is the feedback you need at first. Videotaping a rehearsal is excellent to see if you are clear and concise or if you are talking too much to the group.