When you discover that you're alone on a big stretch of land, try putting a city on a region with water on both sides (a so called choke point) and defend that city with all your might. The land behind is quiet so you can take your time settling and building buildings in stead of units.
My first 25 turns are as follows, mostly as the Japanese (or Chinese for a quick victory):
Found the city and switch to production only. This will produce a warrior on the 3rd turn. Find a barbarian hut for experience and gold (or unit). On the 5th turn you get your second, follow the first. Attack barbarians from hills if possible to reduce casualties and skipping a turn healing. On turn 8 you have 3 warriors out there. Unite the 3 and form an army. Destroy every barbarian village you encounter. If you find a capital before 2200BC, find a hill and attack. Beyond that, don't bother, since they'll have multiple archer units and a backup warrior unit. Unless you're really lucky, you won't pull it off. When the 4th warrior is done at turn 10, switch to science only in the capital. The +1 food on sea regions bonus for the Japanese makes the city grow. Switch tech to pottery and after that, masonry. Masonry gives you a free city wall and at 100 hammers, it costs as much as a wonder to build. Huge bonus! Usually that's around turn 17/18. If you're lucky you've found a friendly village who gave you bronze working and you can start fortifying with archers. Be thankful for the people who attack for boosting your archers with promotions like that
Once you discover mathematics, stack your cities with catapult armies and attack your attackers from within the city limits. Don't go for the military techs right away, but focus on the techs which give bonusses for all your cities, like irrigation, engineering, industrialization, coorporation, religion, literacy.
Another tip: don't build a settler yourself early in the game, but use your 100 gold settler for that. If you're stuck at around 88 gold or so, switch from science to gold for a few turns until you get the settler. After that, switch back to science and build a road to your new city and buy an archer to defend it.