Write and record vocal melodies first. As much of contemporary Tamil music comes from movie musicals, prominent vocal melodies are of the utmost importance and should be central to your composition. Write by improvising with your own voice, then recruit singers to record and layer different parts to a click track in your DAW of choice. Add reverb to your lead vocal to help it sit on top of the mix.
Add prominent drum parts that combine both Eastern and Western elements. Begin by sequencing a driving drum-machine beat with an Indian feel—for example, a beat with kick-drum accents on the downbeat and on the "and" of the second beat. Supplement the drum machine with commercial samples of thappu, a folk drum from Tamil, or tabla, a goatskin hand drum found in Tamil and throughout the Indian subcontinent.
Add a mono-synth bass. In Tamil film music the bass often plays an almost entirely rhythmic—rather than melodic—role. Align the notes on the bass with the kick drum hits in your drum part so the bass and drums reinforce each other, and keep the melody as simple as possible.
Add synth strings or sampled strings with a cinematic vibe. Some of the leading commercial sample libraries offer "cinematic" strings, or string samples that are recorded and processed to evoke the lush, vintage sounds of a studio-era Hollywood film score. Load the samples into your sequencer and use them to write a fast-moving melody that alternates between quick runs and long pauses. Add accents in the same places in which you accented the drums and bass to strengthen the overall rhythm of your piece.