Part 1: Choosing The Starter---When choosing your starter you must ask yourself: Do i want to defeat the first gym and thats it for a while? If so choose Trekko....hes a grass type which certainly means he will be effective agaist rock but not much else until the final gym. Its a shame...really Or do I want to have a very very balanced pokemon with a semi-tough to tough time beating gyms 1, 6, 7, 8, (which you likely will anyway, at least on 6 and 7) in which case go right ahead and choose Torchic....BUT if you want a very good, well-rounded pokemon the OBVIOUS choise is Mudkip which (incedentally) who I'll be following in my team builder.
Part 2: Rustburo City Gym--- OK we all know that Mudkip will dominate this gym...provided he knows water gun...But hold on!!! Wait dont. Thats it...Own at this gym and catch yourself a Tailow up by the mountain in the grass.
Part 3ewford City Gym---If you havent already, by this time you should've trained your Tailow to at least 13 or 14 and your Mudkip to about 13 or 14 also before taking on this gym. With Tailow's wing attack and Mudkip's water gun and the like you should easily dominate this gym.
Part 4: Mauville City Gym---For this gym it is also really quite simple....train your Mudkip to a Marshtomp (awesome bonus becomes a ground and water ) and get your Marshtomp up to 25 or so to learn Mud Shot (key at this gym) and blow away the electric types.
Part Five: Lavarige Town Gym---Also REALLY REALLY simple. Destroy the Fire types With Mud Shot and Water Gun and keep Tailow out of it unless nesiccary. Your Tailow should be about 21-24 and Marshtomp should be 26-30. Catch yourself a Machop on the way down the Jagged Path.
Part Six:Petalburg City Gym---See this is why you have to catch a Machop. He should be at least 24 or 25-27 to take on this gym. Use revives and super potions to win (you probably will need them) (in case anyone is wondering and they didnt read up top, I'm ONLY doing a walkthrough on gyms, nothing else). Tailow should be a Swellow now (24-27), Machop should be 26-28 now and Marshtomp should be 32-35. Teach him Surf...This is a MUST!
Part Seven: Fortree City Gym---Catch a Manectic in the grass across from Mauville City on the right. You may also want to get a Good Rod from the Fisherman farthest north on the beach and catch a Carvahana....Note this is optional...you hear me?!?!?! OPTIONAL!!!! Ok now train your Swellow to 26-29, your Machop into a Machoke (32)-35 your Mashtomp into a Swampert (36)-38 your Manectric to 30-34 and your Carvahana to 26-30. Use your Manectric to its furthest extent by getting the TM Thunderbolt and using it to crush each of the flying types except Altaria, which is part Dragon. For that use Swapert and Surf to wipe it out and you should have no problem whatsoever.
Part 8:Mossdeep City Gym---This will most likely be the hardest of the gyms to defeat, although it still is kinda easy if you know how. First of all you must train your Carvahana to 36-40 (I know drastic) in which case it will evolve into a Sharpedo. You also must train your Machoke to 34-36, your Manectric (in preperation for the next gym) to 36-38, your Swampert to 40-42 and your Swellow (which you need little use of and optionally can be replaced) to 29-32. You will need to teach Sharpedo Surf as well. Use Surf by Sharpedo and Swampert and Crunch by Sharpedo to wipe out your enimies in this gym.
Part 9:Sootopolis City Gym---I know what your thinking; Finally at the last gym....And yes, we are. There is naught you need to do if you have trained yout Manectric to 36-38 but train him or her a few more levels (40-43) and teach or have him or her learn Thunder. Blast your way through the first pokemon untill he busts out a ground/water type (wow like the Swampert) and bust out yourself, and option between your Sharpedo (40-44), Swampert 44+ , or your Machoke 40-42+. Then comes his Draking...Your thinking: I can just blast him away with Thunderbolt or Thunder right? Wrong. Hes part dragon so if you choose to keep Manectric out the he'll keep on using Double Team and Rest to bore you into submission. To not get owned by this, you should or should HAVE I should say teached Sharpedo Rain Dance. Yes laugh if you wish but although it raises water attacks a side effect is awesome: Use thunder and it will ALWAYS hit when it is raining...ALWAYS. Anyway do that and you've won.
Part 10: The Elite Four: Part i--- This part of the E4 is Dark oriented. Use your Machoke (which now should be 42-45+) to kill the pure dark types and the grass/darks, and heck even the sharpedo that gets busted out. If you haven't, you should've bought revives, Super Potions, Hyper Potions, and all the like
Part 10: Part ii--- This part of the E4 will probably give you the most grief. It is all ghost types but luckily you have your Sharpedo and Swampert to get the job done (46-48+ for the both of them ) Avoid Thunderbolt...I dont think it'll happen but all the same: when Shapedo's out aviod it.
Part 10: Part iii--- This Part of the E4 is simple...She's Ice and Water. Use Swampert on the pure ices (two Glialies) and use Manectric (48+ at least) on the rest.
Part 10: Part iv---I was wrong: this part of the E4 will give you the most grief. Rely Heavily on Swampert and Sharpedo. You should've taught them Ice Beam and Blizzard. Use them to win.
Part 10: Part v: The Final Batlle---The last guy is water and you should know what to do: Blast those sons of out ofthe way with Manectic when they are pure water and for the rest use Marshtomp and Sharpedo to own.
Part 11: The Last Part---If you have any questions or something you can contact me at QOTSA.firstname.lastname@example.org
anyway i think you did a good job doing this is realy good