1. Getting the C4 sticky. This can be done via Up Throw chaingrabs (which Snake has on most characters), via Cypher (if you get the second electric shock to connect at low percents you can get stickies), via crawl atttack, via SHFFLing the first two hits of nair, down throw read roll/get up and sticky, down air at lowish percents, via jab resets, and tranquilizer. Learn how you can incorporate Tranquilizer mixups to land them (like say fall through platform, or from a ledgehop, or as a move to cover your landing).
2. Learning your neutral game. Snake's neutral game is basically lobbing grenades at far range, and DDing at mid/close range. Snake has a fairly effective DACUS thats one of the easier ones to perform. You can DACUS out of dash dance. Snake's neutral at mid close range is mixing up WDs/dash dance timings and distances to throw off the opponent's spacing. If the commit you punish them. Sometimes (and I mean SOMETIMES, this is highly unsafe to do, if it is blocked, its a free shieldgrab) you can just run in and go for the dash attack/DACUS. It can catch people off guard sometimes. The DACUS is especially quick.
3. Snake's punish game.
Snake has the best punish game in Project M. It is reliable, and it can kill VERY early. The most common punish at high percents (90 and above) is up throw into C4 detonate. However Snake has much more damaging, more powerful set ups. Forward air/dair into jab reset (if they don't tech) into Tranquilizer into Sticky into down air (all 4 hits) or SHFFL nair (first two hits). If you dair, you could do up air into C4, if you SHFFL nair you could probably regrab into up throw, read DI and fair (and then go back to your jab reset tranquilizer, but no sticky, just do an aerial or grab) or up air (and then C4 detonate).
Another thing to note is that Snake's landmines are hitboxes and free combo follow ups. Look at
this for a better explanation.
Pretty much the 3 most important things as Snake.