If you dont want to start with cloth armor and 5 pots you could start with dorans shield but remember that with this specc and masteries any other items would be a bad choice becuse you need the defense in early game. Razors is also very useful for farming on your lane. Remember that this build do not work really well in mid but at bot it work out really well.

Madred's Razors is good for red buff if your jungler dont need if you even have one.

The reason why i use improve ignite is becuse the ap you get from using ignite makes it easier for you to go for a early kill, you pop ignite and explosive shot that will make alot of damage.

The reason i use health quints is becuse tristana is really sqishy in early game thats actualy the only reason.

Tristana and Garen do insane damage in early game so you should wait until lvl 2 and then garen should stay at lane and tristana go in at the bush that is close to their turret and then wait out until some one of them do a mistake or just go out to long. If they just play careful and wait at turret you should just start farm them out.

I do not use ignite and flash on garen becuse almost always you falsh in and go for the kill and they flash away from you. thats why i use ghost so you can easily chase after them and exhaust so your team mate can come and get assist and also to slow them down ofc. The reason why i use flash on tristana is becuse its very good when you need to get behind them and ult them back and get a kill. And also if you get ganked and exhausted then your Rocket jump will be pretty useless but it helps if you Rocket jump and flash.